Actually the only tractors with 28's after 1951 were the VAC-14, VAO-15, and VAS. The VAH had 36" and everything else was 34", part of the new styling. The 34" rims and centers can be a real bugger to find. Before 1951 with the old body style they offered 32" and 28" for the row crop tractors. 32" are another harder to find size. I used to buy a lot of used tires but with prices of everything going through the roof I usually end up buying new. Either way you got a good deal. The tire paint looking stuff is exactly that. Those look like a "concord" brand tire or an older "armstrong" and they used a paint like release compound for the molds. Over time it gives a cracked or peeling look. I have an 11.2-28 on my 1950 single front VAC that has cracks you can slip a quarter in pretty deep, been running those tires on the farm for years that way. I had them on my 1944 chicken roost VAC but finally found a solid set of 32" rims so it got new tires last fall.