I measured the wheels for my 68 caravel and everthing would seem OK except this inset thing. Looks like the wheels are 15 X 5 with 5 on 4.5. The hub hole is just shy of 2.5. Could the inset be 1 inch. I don't find 1 inch inset wheels on the wheel sites.
The simplest solution may be to take one of your wheels to your Good Year tire dealer and ask him/her to measure your wheel to determine what it would cost to order replacement rims from him/her. This is the process that I followed with my '64 Overlander (actually took the coach to the dealer to have him specify wheel and tire combination) and it worked very well. The big advantage is if the dealer makes an error in measuring it is his/her responsibility to solve the problem and not yours. Given the clearance issues with many of the Vintage single axle trailers, you might want to take the trailer to him/her and ask the he/she measure the wheel/tire combinations and recommend a new set of tires and wheels - - that way if either the wheel or tire has clearance issues it will be his/her responsibility to solve the problem.
Good luck with your tire/wheel selection!