I'd stick with the ready made 1 ton.

Here are a few issues... If you widen the bed it won't look right behind the cab. Running boards will be tricky to make fit and look right. Small truck rear fenders may not be big enough to fit nicely over a 20" wheel/tire.
Just sounds like a whole lot of work for something that may turn out looking kind of funny, and won't be much if any better than the 1 ton you're trying to mimic.

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-