Low vacuum question

fishy. That could be a little tuff trying to balance power with mileage. I think you'll do OK with that. The thing is stall converter speed vs. driving RPM @ set speed.
I don't know what your stall is, but, heres why.
If your driving under the stall or where theres alot of slipage, the tranny heats up and could cause problems and possible failure.
I will have to step back here on this one a bit due to lack of automatic trans exper. and not knowing your stall. Mostly a 4spd guy.
I think it's doable and close enuff in order to be able. The car is lighter than a truck with makes it easier on the trans. and the rest of the build doesn't look like a stressful one.
Reguardless, add a tranny cooler and deep pan from MoPar and run with 27's.
Mopers and BJR's cam choices are really nice if a change comes your way.