Three wire alternator on a two wire system?

I should add that you can get an electronic Vreg that works with your 2-wire system. The advantage is that you don't need to change any terminals at your Vreg or run any new wires. I bought them for ~$11 at rockauto. They are thin and chrome. You can get original looking ones (ugly black box) for a bit more. Search posts here for info. I am not positive that those can handle the field current of a 50 A alternator, but I would expect so since I think the change was in the stator wiring, not the armature, at least J.C. Whitney sold upgrade kits that swapped stators.

Just so you know your options, for your small block you can get a new "ready-to-run" HEI distributor on ebay for <$50. You can also grab the HEI parts from any GM 85-95 V-8 truck at a junkyard cheap (I did), including the GM cable that runs to the coil. You would still need an electronic distributor (ditto w/ TrailBeast's parts), so can't beat the HEI distributor.