So the dyno will set you free......
When you dyno you will end up with the HP and torque curve for the engine.
If it were pure race, you'd likely gear for trap speed, but being a street car, a bit of spit balling is likely in order. I would probably gear for OD cruise at where you anticipate it would be comfortable. For example, my 489 with a upper 240s cam, we started at OD X final at 2.36 and it was a little too tall, so it ended up at 2.63 using 4.11s. and a .64 OD
For yours, 2.63 will be too tall, almost guaranteed, smaller motor, bigger cam, bigger car, a 6R80 has a 4.17 1st and a .69 OD. There will always be enough 1st gear, so say you go for a 3.00:1 compound in OD that would be a 4.33 gear in the rear, likely pretty good, especially if you retain a lock up converter. However, be sure to run a good balanced driveshaft because it will be spinning fast on the highway
I sure wouldn't go lower, because 1st is so low, but 1st being low in an automatic isn't as bad for a street car as a bad OD choice because it can shift very quickly. Lets say you wanted taller gears, and you went 2.87 final, a 4.11 would be pretty close. I wouldn't go taller than a 4.11 though, it does tame down 1st a little, but the the dyno will tell you if it will be happy. My gut says 4.30s for that combo even though 1st will be so short
As far as the converter, after you pick a gear, know the weight of the car and have the torque curve, you call a good converter company and they give you what you need. In your case, I suspect the converter will be loose, but as long as the lockup works, it won't run hot when cruising long distances, but failure to run a loose converter with that cam will likely make it very fussy to idle and worse to drop in gear at the rpm the cam wants to idle at. The converter does two things in this case, loosens up for idle and when in drive, and creates torque multiplication for an engine that may be soft due to the big cam....both good for you.
So, short version....dyno > gear choice > converter > cool tranny as required. Don't jump ahead