Karen, I'm pretty sure the metal stands you have bolted to the frame will work fine with a BBC. Just be sure to use brand new Motor mounts to bolt into them. I got Energy suspension polyurethane mounts that are great. Good luck
I think that the 68-72 frame mounts are the same for bbc and sbc, just like 64-67. I also recommend the poly motor mounts too. I use them on my 396, and they are worth every penny of their $35 (a piece) price tag. They have all of the rigidity of a solid, with none of the vibration.
I just did this swap on a customers '69. The big block will bolt to the frame stands for a small block just fine but the firewall clearance is a little tight with a HEI, but it does clear. Comparing his car to my '68 which is an original big block car showed that the big block stands move the motor slightly forward compared to the small block stands. Make sure you get an oil pan designed for the Chevelle chassis, Corvette and Camaro pans usually won't clear the crossmember and don't have the reliefs for tie rod clearance.
A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more!