The gas tank skid plate is a problem for all wagons '80-on. Debris gets between the plastic tank and the frame and rots both the skid plate and the frame. Be sure to check that the frame is solid in that area. Vehicles from the rust belt are worse off in this regard.
In 1980, Jeep went to the plastic fuel tank which was supported by the skid plate. The tank was then strapped down to the skid plate. We recently had a thread covering this
viewtopic.php?t=23623 where I suggested that the poster find someone locally to make one for them. Other responses pointed to previous posts where the owner suspended the plastic tank somehow and eliminated the skid plate.
MTS makes a tank for a '79 that they suggest can replace the factory tank in these '80-on wagons.
http://www.mtscompany.com/J-truck.htm A recent conversation with MTS revealed they expect purchasers to eliminate the skid plate and suspend the '79ish tank with straps they supply. To me, this suggests that the MTS tank is strong enough to be suspended by straps, but possibly the factory plastic tank is not.
If you want to try and find a replacement, realize there are more GWs out there in need of this part than there are donor wrecks with a good one. If you are in the South or West, you could try car-part.com and look for a donor. You could also try posting in the WTB section here or at IFSJA, or look through the parts cars being dismantled in parts for sale.
Note that you can put a gas can on the cowl and run the engine by siphon pressure alone. BTDT. This will let you run the car for longer than a few seconds. These cars often suffer from very low hot idle oil pressure, so getting it up to operating temperature will tell you something about the engine. With a bad fuel pump (and pouring gas in the carburetor), suggest you pull the dipstick and check for oil dilution; check smell and level. Change the oil first if you find evidence of gasoline in the oil.
The '89 TSM is free to read and download here
https://oljeep.com/edge_parts_man.html - the '91 book would be better but not free. See BJ's.
https://bjsoffroad.com/1991-jeep-factor ... ce-manual/
First post - welcome from Boston!