There should be a casting number on the rear case like R 10 H 1, if it has a rear mount pad it's likely correct for the 63 truck. The earlier version (55-57) car and truck had no rear mount. If it has the solenoid and governor it should be a good find.
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