Since the .21 is a big block you will probably have to redrill the chassis and you could use the original mounts, i put a .26ss in a mamba and i had to change the mounting holes in the chassis, we also have adjustable motor mounts that may work good too. You will have to use a different flywheel, clutch shoes and a clutch nut, when you are ready, i will give you a list of stuff you will need, i have all that you will need to do it.