My current S/P Cuda has a Mark Williams C.M. 3.0 x 42.5 center to center long driveshaft in it, the car had 5.86 gears in the Dana 60 and ran 7.80s ET at 187.+ MPH with a Blown B1 motor on methanol alcohol running 16x33x15 tires on a 15 inch wide rims, I'm not sure what the driveshaft RPM where back then I changed the rear gears to a set of 4.56 and the car now runs 9.0 ET at 147.+ MPH with a set of 14x32xW on the same rims
My message is your way better off buying a better driveshaft than you need now than find out later you need a better one when you hop the car up some more later
Safety gear selection should be like selecting a brain surgeon, don't go with the cheapest one you can find