tha pancake balancer is for a steel crank and the big one is for a cast crank.You will also have to make sure you have a pilot hole in the crank,or have the machine shop drill it for the pilot bearing.If you get these mixed up like the previous owner did with my car they will rattle your teeth.I want to pull my numbers matching motor anyways to preserve it,once its gone the car drops in value.I already have a fresh 1970 340 with all the goodies to go in its place,I just wanted to make sure i was getting the right info before i bag the original and put in my play around motor.An auto has a flexplate and a manual has a flywheel that the clutch grips on to for shifting gears,they look totally different