Depends on what flavor of smallblock, 360 will require an imbalance weight on the torque converter or a external balance flexplate.

Best find someone that knows Torqueflites to beef up the PB one.

As for the manifolds, you will need to mock up the 273 units, I had to grind the head some with my 87 318, but I dunno how it fits on a Magnum.

I am actually test fitting a set of magnum manifolds on my 65 Cuda, which if they can be made to fit are much better than the 273 stuff.