Don't discount the 19.5" options just yet.
Here's a picture of my 1 ton with 8x19.5" tires.
http://rides.webshots.com/photo/1484236297080251109lCqQCo
I think they are as tall as you can fit under the fenders at stock ride height.

You don't want the wheels I ran, but you can find very nice and original looking single 19.5" wheels in the junkyards (I know where s set is, but already spoken for, point is they are out there)

Or for new wheels you can get them here, but they don't look as original as I would want.
http://www.ricksontruck.com/wheels_gm_srw.html

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-