Like said above. You can use the I6 towers for the V8. You don't even have to move them. Get new rubber mounts, why use old ones. My 66 was an I6 Truck and I never touched the towers and just dropped in an 87 year model V8. The 66 towers will bolt up to the newer crossmember without even drilling any holes. Was done when I helped a friend with his front crossmember swap.
Here are some pictures of the V8 sitting on the I6 towers. I put new mounts in because the others were falling apart.
Check out this thread with all the pictures and all the stuff we did to get it done.
http://www.chevytalk.org/fusionbb/sh...hp?tid/223597/