Trucks normally had a steel gear so it is likely your truck has a passenger car transmission or at least the rear housing and the gear.
Cars and trucks with OD used the plastic gear. The long shaft white gear is available on ebay for about $10 from Muttonhollow Chevy's in Utah. If you found it at ecklers that would be fine also.
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