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

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!