Tommie those are two different castings. The C6-R's have 71.2-74.2 cc chambers. Guys call them the "poor mans CJ heads". They are also a low riser casting. The D2-AA is a 72-76 truck casting common to the 360/390's. The chambers are smaller at 68.1-71.1 cc's and they have hardened valve seats for unleaded. They are also a medium riser casting. Both have different size intake ports. Pretty much a mismatch for sure. G.