need help with engine swap

With a 360 you need a counterwieghted damper and flexplate. No amount of fluid filling will make up for the weight. Yes, a 360 can be balanced internally, but this will require adding heavy metal or lightweight forged pistons (extra $$$). But why? You were planning on adding an SFI approved flexplate while you had it apart right? 360 weighted flexplates are pretty easy to come by, and then you can run any converter. Same with SFI approved 360 crank dampers. The engine doesn't care where the counterweight is, so long as it's there.

If it were me, I would probably use the 360 you have now. OR, if I was going to swap in a later Magnum engine, I'd go looking for a 5.9. In either case the stock exhaust manifolds on an early-A only support about 250 HP, so I'd save up for decent headers ($$$).