Not sure the sm420 will bolt up. The bell housing bolts are a different spacing. If you change bell housing you will loose the pivot for the brake and clutch!
Not much for trans options without major fab work.
I'm going through this on my 4bt swap on a 44 1.5t. The engine needed a newer bell housing(from a sm420 trans) the bolt holes didn't line up with original trans. Then I noticed the clutch and brake pivot didn't have a spot to bolt up to. Now my current plan is a 4l60e from 01 blazer and stand alone controller with brake pivot from 49 1.5t frame. Not sure how that is going to fit yet!
Rh
