[Jeff Lee]

Just to make sure we're on the same page, I see a 1971 Torino SW with a 351C-4V that is factory rated @ 285 HP. Is that the engine you are going to run? Then it is 305 NHRA rated HP, not 300 HP.
Also the specs are a .430"I / .450"E cam, Not .420" / .450".

After looking at what GTXJohn said about gearing (he runs SBM which would have a lot more bottom end than your Clevland), I would start with 5.38's. And you might be right on about the 5.57's.

I believe Pro-Trans will build a TF inside a C4 with better low gearing. Of course that isn't cheap!

For a wagon, I think those are pretty cool. Not Vista Cruiser cool, but I think next best thing.