I have a 37 Chevy Master (Driver) that has a 350 Vortec engine in it with 4bbl Edelbrock carb, I don't know what rear end it has on it, but believe the ratio is 3.1. Currently when I drive, at about 50 mph, I am running about 3600 rpm, watching my gas gauge scream down. I don't want to replace the rear axle or gears, if possible, and believe I have a thm-350 3-speed transmission installed. I am wondering if I can replace the transmission with either a 700R4, or 4L 60E, and would a 4-speed overdrive be a good option, and will they bolt up. Nothing on the car is electronic and it is an automatic on the floor. I bought this as-is and know nothing about it, so am grabbing at straws. Any assistance would be appreciated. Jim