Anyone can correct me if Im wrong. 16.5 wheels were very very common on 3/4 and 1 ton of the 70's and early 80's. Im pretty sure GM put steel 16.5's on from the factory. The reason (like I said, correct me if Im wrong) was due to larger brake calipers on the front and larger drums on the rear. You stated you have a "camper special". Meaning it will (from the factory) have a heavier rear end/springs and probally larger and heavier front springs(4x4)/coils(2wd) to accomidate a "bed camper", gooseneck, 5th wheel, bumper pull campers. Usually those trucks had a larger motor, usually a big block of some kind, and heavier trans, auto 3spd or manual 4spd. If you want to go to a 16" rim, try finding a stock one at the junk yard and try it on all 4 corners of your truck to make sure there are no fitment issues. Worse case you have to jump up to a 17", which most new chevys have stock, and have a LARGE selection of tires.
Just my $0.02
Hope this helps you out.
John