Let's see a picture of those wheels.
I remember now having owned a set of 8 lug 19.5 duals with an uncommon center style. They were more cone shaped, these might be what you have?
The 19.5" wheels that fit on my truck, and most all that I see out there have a concave, spherical shape to the center dish.
Wheel adapters or spacers just sound like a bad idea, and expensive.
Also, have you considered a 14 bolt rear axle swap to get faster gears and more modern drum brakes with available replacement drums on shelf at parts stores still?
That would likely also solve the problem and let you use wheels you have.
Grigg
