Since you also have an open driveline that is used with the transmission posted by mechanic 58 there are many options. The Saganaw as stated previously, the OD version of what you have which is an SM 319, a T5 and others. There are parts available to repair what you have but it could get costly.
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