Same column ,same torque tube ,I don’t know what the difference is in mounts for the tranny but the Sm420 hangs off the bell housing and I think the 3 spd has a cross member .The transmission cover is different ,has a bump and the hole for the shifter. The steering seal on the column is different 4 spd is round with the hole for the column the 3 spd has another hole for shifter rod.The Two transmissions have the same final gear so will drive the same 1st gear is basically a parade gear as you can walk faster on a 4 spd and is also 1st gear is non synchronized so you have to stop to go into 2nd or start in 2nd gear.
