Wheel Question: Backspacing, Max Size, etc

[Tmwoodall]

So I bought these wheels when I was 17, and the guy told me "They don't fit your truck" we argued back and forth several times and he sold them to me. Technically they fit, on the lugs and over the center dust cap. However I think the rear is off in terms of backspacing, and could be wider to give it a more aggressive stance.

I don't have a good pic of the back, but there is about a 3 inch difference from front face of wheel to edge of fender. Is that a backspacing issue? Or is that totally normal and acceptable?

I think I am going to change up the wheels entirely and get a wider wheel (currently both 20 * 8.5") and maybe increase the profile of the tires. Plus my taste has changed from 17 > 25.

Second question, what is the max size I can run with the ECE 2.25/4" drop on a 72 Axle (already installed)? I have been searching and can't find exactly what I need.

I really like the look of the Boss 338, a LOT. But the fittment issue is going to keep me away until/if they fix that. So I am still searching, and may even drop down to an 18"... Any and all input/pictures would be greatly appreciated.