My 1929-51 Chevrolet Parts Book Group 5.441 confirms 1947 1/2 ton trucks are a one year Propeller Shaft, 65-7/16" long with 17 splines, p/n 3683172.
For comparison;
1941-46 1/2 ton shafts are 61-1/2" long with 17 splines, p/n 3657323
1948-up 1/2 ton shafts are 63-7/8" long with 17 splines, p/n 3694764
Mike B
