I'm sure HevyHauler can give some more clarification on this since he's already done this stuff, I'm still workin mine out so this is a topic I'm lookin into as well.

To save some bones, you can register it at 16K, and buy tonnage on short term basis for when you're actualy going to be on public roads with it.

The trucks came out of the factory with lighter duty axles and springs, thus the 16K GVW on the door, I have the same deal. However, if you look up a few things you'll find that when the chassis was sent to the finishing company they would swap out the axles and spring for heavier weight capacity parts, esp. on dump trucks. The factory data I have found on my '56 says I should be able to take it to 21K, but I need to verify my rear axle as I believe it's a 24K unit.
Once you have all that down, then it's up to your tire capacity, I need to find the formula and pressure to weight charts for my tires so I dont get popped (maybe literaly!). Should be fine tho as todays tires are a darn sight better than back wehn our rigs were built.

As for insurance, I had to insure it as a comercial vehicle, nobody would touch it otherwise (BTW, Farmers was the cheapest I found that could cover everything I needed to insure). Now that I'm starting to use it for a business tho, kinda worked out.


1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion!
:P