Or in addition to what I just typed, use the TH400 and 2.78:1 diff with the EFI top end on the 308TH bottom end. Easier again. You won't need to worry about gas if you have the EFI engine. With gas about half the price of fuel it'll cost about the same to run, an EFI 304 in a HJ would pull 25-30MPG with a mix of driving. You'd be lucky to get half that on gas with an old carbied 308 with an older style system.