Don't think you have told us what size truck you have yet?
If it's a 1.5 or 2 ton then 20" wheels are stock.
If it's a 1 ton then 17" single wheels, or 18" dual wheels are stock.

If it's a 1/2 ton then I can't think of a good reason to use 20" wheels, probably not even 18" wheels.

Take a look at trucks like yours, and like you want yours to look, if you can "preview" your ideas on someone else's truck it may help to decide what you want.

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
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-