Van front does me no good as it ain't 4x4, and the rear (desirable for the disc brakes) won't line up with the truck springs.
I don't think I'd trust any machine shop for welding up two cast hubs together, it's just one of those things only a welder with years and years of experience could do. What I would trust is billet steel adapter rings, but those are also a custom job, however much simpler.
The 3500HD Chevy uses 19.5" wheels, yes, but they are not 8-luggers - they have 10 holes in them, the rear axle uses 10 studs so all the holes are utilized, the front I-beam has only 5 lugs per wheel so half the holes remain empty with the wheels bolted on. The only factory 19.5" 8-lug Chevy wheel that I'm aware of came on the P30 cutaway vans (the ones with a setback front axle), and they will not clear the Ford hubs without machining the center opening out a bit.
As fpr aluminum adapters being junk, "guaranteed" at that - well we agree to disagree on that, as I have seen what some people put their cars and trucks through with those, and it's more than I'll ever push any of my vehicles.