With a blown motor especially a BBC you will have no need for the deep 1st gear of the 700r. The T-400 is a good choice with a good rebuild and a shift kit.

I think you will have tough time keeping the 700r together with a blown bbc in any car.

I use a T-350 in my blown sbc Willys and would have no need what ever for a lower 1st gear. Mine has got 7500 miles on it in less than a year. Probably 1000 yards of burnt rubber. haha

Dollars and cents wise you can buy a lot of T-400's for what you will have in any OD trans.

Keep in mind that the OD will only be good if you are cruising at 65+ . Below 50 it probably won't engage anyway.