On the SM420(original 4 speed) transmission, you can use the "open" drive later with a torque tube. If you save the "tail" off of the older transmission. It bolts to the same pattern with out modification. The "ball" casting is bolted to the rear of the casing in the same place as the "seal" casting on the newer transmission. Same applies to use of the older SM420 in an "open" driveshaft. Just change the "ball" casting out for the "seal" casting and in it goes. I never, ever throw stuff out like this. Has saved me many times. You can use the 4 speed from 47 to early 60's if you need to. One part and all is good. I have not tried this with the 3 speed so no advise or opinion for that.
