When Tamiya did a rerelease of their 787B kit in 1999, Studio 27 released
no less than 4 different sets of decals, covering all 787 and 787B liveries.
Scale Motorsport has released a set of composite pattern print decals and a very
well detailed set of etched stainless steel parts, both designed to further enhance the looks of the Tamiya 787B kit.
In June 2002, Museum Collection released a set of Hi Tech decals designed as a replacement for the decals in the Tamiya 787B kit.
In addition to this both Studio 27 and Modeler released an etched stainless steel detail/upgrade set,
the Studio 27 set contains some parts to help converting the Tamiya 787B into a 787 model.
Note however that there are many differences between the 1990 787 and the 1991 787B,
the most noticable ones being a 25mm increase in wheel base and a reshaped rear deck.
I have to dig a bit deeper for exact details, but I think a spare Hasegawa 767B will prove
very useful for converting the Tamiya kit to a proper 1990 787.
Especially during the 1991 WSC season the 787 and 787B cars were changing colors
often and the two types are difficult to tell apart. Some clues for telling a 787
from a 787B are:
Note that during the 1990 season and early in the 1991 season up to the Le Mans 24hrs race,
the 787's were fitted with 17in wheels similar to those in the Hasegawa 767B kits.
Starting with the Le Mans 1991 race both the 787 and 787B's were fitted with 18in wheels.
A good source of info on the development of the 787B is the book:
"RX-7 The Mazda RX-7: Mazda's Legendary Sports Car" by Jack K. Yamaguchi and John Dinkel, Ring Ltd. Japan,ISBN 4-947659-01-7
Studio 27 has released the following decal sets:,
At 1600 Yen, these decals are pretty expensive (same price as the entire Tamiya 787B kit) but printing quality is excellent.
For more info on the Decals and Upgrade Sets, check the japanese online shops on my links page.

released in July 1999
Set 209 covers 787 chassis nr.001 in its 1990 Le Mans 'Art Sports' livery.
This car failed to finish the 1990 Le Mans race due to an oil leak.
In addition decals are provided for an unpainted test car as it was driven at the
Fuji race track in preparation for Le Mans.
All decals are provided to do both versions (although you have to add about an acre
of carbon fibre print for the test car, Scale Motorsport sheets 1024 and 1020 are perfect for this).
You can find a picture of an unpainted 787B on my car reference picture page.

released in July 1999
rereleased in June 2004
Set 210 covers the 'white' 787 and 787B that competed at Le Mans in 1991.
Note that nr.18 is 787B chassis nr.001, whilst nr.56 is 787 chassis nr.002 fitted with 18in wheels.
Nr.18 finished 6th and nr.56 finished 8th overall at the 1991 Le Mans race.
These decals can also be used for depicting the nr.18 car as it competed in
most of the 1991 Group.C cat.2 World Sportscar Championship, do note however
that this was 787 chassis nr.002, not 787B nr.001 !
The blue lines around the cabin are also provided as decals, the only decals
missing are small 'T' symbols that would allow for making the spare car nr.18T
(787 chassis nr.001) entered at the 1991 Le Mans race.
Decals are provided for one complete car.
The 2004 rerelease of this set has newly printed instructions and the decals are now printed by Cartograf.
Although the layout of the rereleased sheet was changed, the designs are identical.

released in July 1999
rereleased in June 2004
Set 216 covers 787B chassis nr.001 that competed in the 1991 season of the All-Japan Sports Prototype Championship
(JSPC) after it ran the 1991 Le Mans race.
The green parts of the color scheme are all included on the decal sheet, apart from the rear wing, which has to be painted green.
Note the typo in Johnny Herberts name (J.HERBART), you have to replace this decal with the one from the Tamiya kit.
Decals are provided for one complete car, with a choice of racing numbers (18 or 201).
The 2004 rerelease of this set has newly printed instructions and the decals are now printed by Cartograf.
The layout of the rereleased sheet was changed and the names for the drivers are now printed in a slightly smaller size,
but Johnny Herberts name is still spelt wrongly as J.HERBART .

released in August 1999
rereleased in June 2004
Set 228 covers 787 chassis nr.002 in its 1990 Le Mans 'Charge' livery and 787B chassis nr.003 in its 1991 JSPC
'Renown' livery. 787 nr.002 failed to finish the 1990 Le Mans race due to electrical problems.
Note the typo in Johnny Herberts name (J.HERBART), you have to replace this decal with the one from the Tamiya kit.
No color patches or white dashes are provided on this sheet. For the 'Charge' scheme the green patches can be taken from the
Tamiya decal sheet, for either scheme the white dashes can also be taken from the Tamiya sheet.
Decals are provided for one complete car, although only a couple of items keep you from completing the scheme for the other
car as well, borrowing those items from the Tamiya sheet allows you to do both schemes.
The 2004 rerelease of this set has newly printed instructions which include a full color photograph of 787B nr. 003 in its 1991 JSPC livery.
The decals are now printed by Cartograf, the layout of the rereleased sheet was changed, a pair of decals with the name of Y.TERADA
were added and the names for the drivers are now printed in a slightly smaller size. Johnny Herberts name is still spelt wrongly as J.HERBART but
his name is not on the cars in the instructions.
By combining sets 210 and 228, one more version can be recreated: During the 1991 JSPC series 787B chassis nr.001 was seen wearing an interesting variation on the white/blue scheme, with a blue 'Renown' text (outlined in white) on the nose and a white 'Renown' text on rear wing replacing the 'Mazda' text (race nr.201).

released in June 2002
This is a set of Hi Tech decals, designed to replace the kit decals of the Tamiya 787B kit.
The decals are identical to the ones in the kit (although the silver engine hatch patches are not included),
but printing quality and color accuracy are much better. Even a set of white dashed lines is provided.
High Tech decals have a special carrier film that you can tear off the model after the
decal has settled, leaving just the printed image on the model. This is a bit tricky, the
decal image can be damaged in the process so each sheet offers a complete set of spare decals plus
some extras on top of that, so with a bit of luck you can do two cars from one sheet.
released in February 2003
A small set of High Tech decals for the nr.55 787B with additional photoetched steel parts and red ribbon for making seatbelts.
All decals are included only once (no spares), a set of white dashed lines is included.
This set consists of three different decal sheets, each with realistic carbon/kevlar
patterns. The clever part is on the back of each sheet where reversed outlines are printed
for each of the kit parts to be covered. Decals are provided for all exposed unpainted parts
of a 787B.