anybody ever tried an s10 blazer tank in the rear of a 55-59? top fuel pump, side fuel fill. 20 gallons. don't know dimensions though. would leave room for inline filter in the area of the cut off corner possibly? dunno. originally probably was there for exhaust clearance?
https://www.amazon.com/Gallon-Chevy-.../dp/B077JF6CH9
you could use a fuel door or blend in the original filler with rubber grommet in the rear fender for easy fill and no run-back on acceleration. depending on the fuel system, if you need a vented cap, it can always run out those low filler styles that are almost even with the top of the fuel tank. on a hot day a full tank of fuel expands to spill out as well. sure, you get used to it and don't fill the tank to the top, but why not just build it different to not have the problem in the first place. the same for the filler in the box floor. it's great if you KNOW you will never carry anything. if you do it kinda sucks to move stuff just to access the fuel filler.
just my opinion, doesn't mean much.