Quest for the Holy Tire

[76C10Stepside]

My '76 C10 has P275/60R15 tires. When one gives out, I find a good used one to replace it. Was getting them for $20-25, then the last one cost $40. One of the four has been in need of replacement for the last 2 years, but could not find a good one. Well, it finally gave out, and my spare leaks too (rust on the rim). None of the used tire stores around here have one.
I checked prices for a new one, and WOW, they cost a lot. I don't want to pay $175-180 for a tire.

I got a Uniroyal Laredo P235/75R15 TPC SPEC. NO. 2306 mounted on a nice 15x7 5-Lug/4.5" bolt pattern (1/2" lugs), 5.5" backspacing, 2.5" centerbore from a wrecking yard to use for a spare. All the wheels/tires were just laying on the ground. This one was in the Chevy truck/van area, so I figured it would fit (duh), but the backspacing is way too much and it won't clear the brake caliper on my truck. I THINK it's for a Chevy VAN (see photos)? Would like to know for sure. I've never had to add air to it.
This tire is way taller than my other tires, and my current spare is way shorter, LOL. I need one that fits!

Anybody know where I can find an affordable replacement tire?
Looking for a cheap solution here, any suggestions welcome! Maybe two taller or two shorter (yuck) tires? What are y'all who have 15-inch wheels running on your truck? Thanks!