Sounds like you need a 3/4 or 1 ton truck, that would be the simplest way to get the heavier running gear, springs, and even frame.
Every few weeks someone ask how to get rid of the 8 lug axles on a 3/4 or 1 ton because they want the 1/2 ton stuff.
Wait for the next person to ask that question and offer to trade complete trucks or at least from the frame down plus bed and running boards.

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-