Depending on the positioning of the 302 vs the 250, you may need a different driveshaft length ( even if you keep the 3 speed) Some Toploader 4 speeds have longer tailshafts than others ( the Galaxie units are 3 inches longer than the Stang/Fairlane ) There are also different shifter positions on Toploaders for different cars. I would wait til you get the 302 in before buying a 4 speed. Then see if the transmission's position has changed. I don't think it will, but you never know when doing engine swaps, especially from a 6 to an 8. Most likely you will need a 4 speed with similar dimensions as your 3 speed.