Interesting. I suspect the custom 16s fit your drums because of the drop center design of the new rims. We've had isolated comments made that guys have found salvage yard 16s that will fit the 14" drums, but none of the comments contained exact information to allow us to know what donor truck to focus on. It makes sense, though, that your custom wheels could be spaced to allow use of your stock centers. Good to know.
Building custom wheels was the last of Brien's available alternatives, but I didn't get that far with him. It is the highest cost alternative, and one that guys normally don't embrace if used wheels can be found. But, from an originality standpoint, the below wheel can't be beat. It is one of a custom set made by Stockton Wheel for a man named Mike Goldsby using his stock 17" widow maker centers. Because the stock 17s (as I pictured above) have the centers riveted to the "semi drop center" of the widow maker rims, it works out that the center disc fits perfectly into a new tubeless 17" drop center rim. This allows use of stock 7.50 x 17" bias ply tires since they can be mounted on the drop center rims the same as any other modern tires. This is the only example I've heard of where somebody has gone to this extent to retain a pure original appearance. Stu