If you have a NAPCO 4 wheel drive ½ ton, the following might be of interest. Owners sometimes wonder if their NAPCO 4 x 4 was installed at a franchise NAPCO shop that were in most medium size towns or was it installed on a Chevrolet GMC factory assembly line when GM began offering them in 1957. (NOTE: GM first offered 4 wheel drive trucks in 1957 and used the pre-existing NAPCO system) Of course, the letters NAPCO were never printed in GM literature and the NAPCO fender emblems were not attached as they would be by a franchised dealer.
If you have a 1957-59 Chevrolet or GMC, you can always tell if it is a NAPCO system by looking at the front of the axle housing. The N-A-P-C-O letters will be in full view!
Another quick way to tell the source is the leaf springs. From a NAPCO installed kit the ½ ton front springs are not changed but have 6 leaves on the front. The GM assembly line used 7 leaves. On the rear NAPCO installed kit they used the original 7 leaves. GM used an 8 leaf spring.