So this discussion is about a truck used in tractor pull events?
What rear does it have under it now? The factory rear should have been either the HO72 Eaton or maybe a Dana 60. I don't recall ever hearing about a 6.17 available for the Eaton and I don't pay much attention to the Dana options.
Its possible the existing rear can be refit with hubs that will fit the wheels you want. That would be stronger and possibly cheaper than having adapters made.
And since many of the adapters on the market are designed to mount big wheels for looks, I'm not sure I'd trust them in this kind of high stress application.
