I have a '74 Javelin with a 360 and 998 3sp automatic transmission. I'm interested in upgrading the transmission to have either an overdrive or to put a new one in with 4 speeds. The reasons for doing so include better gas mileage and less engine noise/stress. In my younger years I had a '72 AL trooper Javelin with a 401, and it had a fourth speed, but I don't remember what kind of transmission it had. Unfortunately, it's long gond now. Does anyone have any recommendations on the transmission upgrade?