One advantage to the SM 420, besides being tougher than woodpecker lips, is that 2nd. gear is synchronized. You can shift to 2nd. while rolling up to a stop sign without grinding gears. 1st. only gets used when a really heavy load is involved, or starting on a very steep hill. A SM 420 and a 4.10 final drive is a good combination. If you can find a Dana 60 axle and a 3.73 gear like I've got in my 59 Suburban with a 420 trans it's even better.
Jerry
