Is your 3800 a dual-wheel rear unit? If so, you'll find that 16 inch drop-center rims for tubeless tires will not fit over your brake drums. The straight-center lock ring wheels for tube type tires will just barely clear the drums on some models. My 1959 3800 had 18" tube type tires on split rims as standard equipment, and I believe a 19.5" tubeless tire rim was the direct replacement for them. The older step-van bread trucks with a 1-ton chassis ran those wheels, but I retired the truck before I found a set of replacement wheels.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!