Those are the correct mounts to install a .21 engine. However, I found out that only a few .21/.26s will fit up to them. The clutch bell postion still has to be adjusted fore or aft for proper gear mesh. Of my .21 engines only the Ofna .21 would fit these directly and some creative leakage work had to be done. Also, several of my big block rear exhaust .15s work quite well with these mounts.