The torsion bars should hold up on a BBC, since the same front suspension is in the GMC's with the big 305 V6s.

The best spot to mount a BBC is to have a 2 inches in the back of the engine for clearance so there's easy access to puling the distributor, and valve covers.

Also the radiator will need to be a 4core to keep the BBC cool.

For engine mounts, you'll need the engine mounts that originaly came off the engine.
I hope this helps.
David