Some things to consider: You will need to modify the drive shaft to fit the Saganaw transmission. Also, find a 3 speed column with all the rods & levers or install a floor shift conversion. The three speed does have somewhat closer ratios than the SM420 and it is fully syncronized.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine