Which Tremec TKX Do I Get

I would get the 2.87 and the .68 OD. I have a T56 Magnum with the 2.97 1st, 3.23's, and 25.6" tall tires and its just about right for a street car. I'm running a 340, but with EFI and I can pull 1500 rpm and the car is happy, even to go up hills, drive around a lot at 55 or more in 6th.

My engine made 400 lb-ft @ 2800 rpm on the dyno. I should probably have less torque than you do and I like it. The EFI does help with pulling a low RPM but if you want to drive on the freeway at 70, it will run 1900 rpm which is pretty nice. If you only ever go 60 mph, pick the .81