I have run 4.56, 4.11, and 3.91s in my 440 62 savoy, and the car didn't care, it ran the same. As a result, I would lean toward 3.91s, especially with a 512.
727 (no brake. Agree, a brake with an 8 3/4 is pushing your luck), B&M pro ratchet, reverse manual body is what I use too. Good choice, in my opinion.
Not, however, a fan of TCI. It's not for nothing their nickname is Total Crap Inside.
With good cylinder heads (get the biggest/best you can afford for a 512) and your car weight, 10s should be no problem.
And you don't need the weight of a full cage til you are in the nines. Unless the cage is already there, I'd put in a 8-point bar.
For slicks, as big as will fit, and I'd shoot for 4500 stall. Get one from a Quality converter shop, but it won't be cheap. (A good custom converter for my application moved my car from mid 6.50s to low 6.30s, with a brake in a light car, however).
And I just turned 70, you've got lots of time to go fast yet.