When I first bought my cj-8 it had 15X10s with 32x11.5 on it and they ran fine. The backspacing was appropriate for it though. The general rule of thumb is that you can go up to 4 inches wider on your tire than rim so yeah 12.5 inch tires on an 8 inch rim would be pushing it.
I'm actually looking at 285/75/16 for my current 8" wide wheels (are 33.1 tall) or if I buy wheeels like this I could do 33x12.5x15. The tires are a little less on the 15s. Also thought of painting my steelies Grey or bronze.....kinda like the dirty color in this pic