455 backed up with a Tremec 5-speed. Street build; I wont be racing it. What U-joints should I use? I have no drive shaft and 2 different ends I can put in the rear end. I holds 3RL U-Joints and the other is smaller; not sure the exact size.
The largest one, or use whichever one matches the driveshaft you'll use. You will most likely have to shorten a stock driveshaft or have one custom built for use with the Tremec, I got a custom one for mine, so get whoever builds/modifies a drive shaft for you to include a yoke for the larger of the two u-joints. I always went with the largest joint that would fit. Don't race mine either but you never know when you'll grab some good traction while having all that torque applied. I consider the U-joints to be the weakest link in my drivetrain.
I have a driveshaft in my garage you could have, but shipping it from one side of the continent to the other would cost more that having a custom one built there.