Tire selection???
Ok, so that’s helpful. Looks like the wheel is centered pretty well with that backspace. A Cooper 245/60/15 has a section of only 9.5” on a 7” wide rim, so yours probably measure a bit wider than that at the section on 8’s. For race only I’d say you can use about half the extra clearance you’ve got there, so yeah, keep the section width under 10.5” for whatever slicks you want.
Your 245’s are only 26.5” tall, you can see how tight they are to the front of the wheel openings. I don’t think you have more than a 1/2” to give there, which only gets you to 27.5” tall, maybe. You’d have to move the axle back to do 28’s IMO, but I’m just looking at pictures.