I put a 20 gallon YJ Jeep tank in my friend's '86 SWB 4 cylinder. I had to make a new skid plate (1/4" thick bottom, 10 guage sides) and make a new filler hose and hose size adapter to connect to the stock filler neck. A '95 ZJ Jeep sender on the YJ fuel pickup module (with an added resistor) operates the stock gas gauge perfectly.

The stock tank was smashed down to about 12 gallon capacity, the factory tank costs aroung $500 if I remember right. I think I had around $40 in the steel to make the skid, (twelve years ago or so when I did it) the tank came free from a YJ that got a 26 gallon Aero tank. It's taken many heavy hits and only has a few scratches in the skid plate. You can lift the rear of the loaded Montero with a floor jack under the tank! It sits about 1" lower than the factory tank and fits pretty well between the leaf springs. I had to modify the tail pipe to route it to come out the side behind the tire and cut off the original fuel tank mounts on the frame and make my own mounts from 2" square tubing to get it to fit.

My buddy is bringing his Montero over this weekend or the next for me to change the CV boots and rebush the idler arm. I'll try to take a picture of the Wrangler tank installation.