any insights as to the possibility of getting 75+ mph out of a 1981 300 gd? is it possible to regear these drivetrains? what kind of work and what kind of money would i be lookin at in parts and labor if i had a shop do it? is it a diy type project? would an intercooler help with top speed at all? do they make an overdrive for that model? thanks, everyone. everythings a learning process with me, haha.