The well built new 5 and 6 speed rail shifters are rated for 500 to 600 ft lbs torque, some higher if you want to spend the $$$$. Automatics are the easy way out, but you don't have to limit yourself to 3 forward gears and an overdrive....along with all the inherent heat problems that hi stall converters add to the other cooling issues associated with blown engines..... Whatever tranny you get, manual or automatic, make sure it's torque handling capability is equal to the output of the engine. A cheaper tranny may save you money initially but after a couple rebuilds the savings are way deep on the negative side.