The SM420 has a completely different configuration, length, and shifter location than passenger car 4 speeds like the M20 and/or T10. A driveshaft modification would be required and the shift arrangement would be nowhere close to looking original.
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