I would stick with the 700r4.
You can use it in 3rd gear and you're driving around 1:1 same as the th350.
Then when you get on the highway and get up to 70-75 and all the rpm's and exhaust noise start to grind away at you, throw it into overdrive.
At 75MPH, with a 26" tire, rpm's will be 4090.
Throw it into OD and and it drops to 2788.
I'm not sure how it would run at those rpm's with that cam, just showing how a 700r4 could be useful especially with 4:11's.