The guys at Hey wheel can make about anything. A buddy has ordered several sets of rims for assorted hot rods from them, and they can (and have) made whatever he wanted. They build assorted tractor rims. Get some actual measurements and sketches of what you have, and what you need. Clearly label it, then email or fax it to them. I bet they can come up with something, whether a deeper drop center, or build you a new center for the rim to match up with your Ford rims, or something else. I would actually be very surprised if they cannot/will not.
It probably won't be cheaper, by the time you replace the rims, get new rear tires, and then make whatever adjustments the front requires, than it would be to just buy new tires of the same size, even though they are over priced. You'll get 20 years of service out of them, probably. Or, if you're going to wear them out frequently, eat the money and do it properly, with a correct replacement rim of 28" diameter. I know Hey can make an entire rim to match.