Backyard fix
I had roughly the same problem. Broke the plastic piece while trying to replace a fuel line that had rusted thru. Cost of the new tank unit was going to be $300. 00 +. I took a piece of 1/4" aluminum plate, cut it to fit inside the screw on top of the old unit, installed 2 bulkhead fittings (3/8") in the plate. Then I measured to the bottom of the tank, cut a piece of 3/8 copper tube, put a brass tee on the bottom and connected the top to the bulkhead fitting. Then I put a short piece of 3/8 tube on the other bulkhead fitting (return line) and put the little rubber valve from the original unit's return line on it. I then bent 2 short pieces of tubing so they would connect to the feed and return lines on the truck and put them in the top of the bulkhead fittings. Re-assembled an I was "On the road again" I was without a fuel gauge but it never worked right anyway so i didn't really lose anything, and this setup WON'T BREAK!! Hope this helps someone, Max