I assumed the 3500HD is one with an I-beam axle and 10 lug wheels, back when HD meant something. Seems everything now days is HD or Super Duty...

You may use the spring pads off the original axle as it, the Dana 80, and 70HD all have 4" axle tubes.

•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-