I have a 1950 Plymouth Deluxe that I dropped a 251 flathead six into from a 1952 DeSoto. I used the 1950 bell housing, clutch setup and the stock 3 speed manual transmission as it bolted right up and its what I had. I have a chance to buy an R7 overdrive and I need to know if it'll be a bolt for bolt swap. What will I need to make it work properly? Is there a specific model number that I need? I know the R-7 was made for other vehicles but I have no idea which one would fit my 50 Plymouth. I've done some research but the more information I have the better I'll feel about driving 600 miles to get that R7. Thanks in advance.