JD, is there any particular reason you want to use the 4-speed, aside from eliminating the column shifter?
If the main goal is to switch to a 4-speed purely to eliminate the column shifter, and you are happy with the gearing as-is, I'd say forget it and just convert the 3-speed to floor shift as 4ontheFloor suggested. The shifter companies (such as Hurst) make universal 3-speed shifters just for that purpose, and it would be cheaper and require much less work than fooling with a tranny/driveshaft swap. I don't see an advantage to using the SM420, as you'll probably end up driving it like a 3-speed anyway, skipping the granny low 1st gear. In fact, with the SM420, even 2nd gear is lower than the 3-speed 1st gear.
