Swapped my 88 it was origanly the 13.5 gallon tank style. I went an got one from a junk yard because i wanted more capacity, the only thing different was the small tube inside, i think it was the vent tube, it ran right next to the larger fill tube. The 13.5 had a longer extention after i turned down tward the bottom of the tank, the 20 gallon tanks tube stopped right after the bend. Everything else was the exact same on both tanks otherwise. I could never get more than 15 gallons in my old tank, yes and i ran out of gas when i did that.
The skid plate that came off the junk yard XJ (forget the exact year, not above a 92 i remember that) fit my 88 perfictly, everything lined up, i used the same pump, same electrical connections, same fill lines, only thing thats off in it the gauge, but seems you can bend that and it will work.
