[snj8198]

Hi odog,

The '70's to early 80's sm465's had the np205. The 465 granny gear is not quite as low as your 420 (7.0 v.s. 6.55) but regardless it's tough to beat. If you could get your hands on the assembly for a couple hundred bucks ish it would very take little maintenance before slapping it in. I forget the length difference between your 420/221 and the 465/205 combo. You may want to figure that incase you need to address driveshaft length differences.

-steve