Hi, tested installation of RB race .21 (old C5) to see how it will fit.
Parts needed from Amainhobbies:
1 x KYOIF108 Kyosho Stock Engine Mount $7.75
1 x KYOIF107 Kyosho Engine Mount Plates $6.99
1 x OFN10099 OFNA 1/8 Clutch Bells Shim Kit $4.29
1 x OFN18067 OFNA .21 Manifold/Ring Mount Spring $11.99
1 x RCEK8011 K Factory Hard Coated 3-Shoe Clutch System $24.99
Of course you can opt for all Kyosho parts if you like.