From 1947-55 Chevrolet had no 1/2 ton "long bed" truck model (GMC did, for some, if not all, years).

Curt's observation about 8 lug vs 6 lug is important.

Is the indentation in the fender needed to mount the tire, or, is there more than a inch or two of space between the spare tire and the indentation (an indication you have a long bed)?

Tim