I searched here and on other forums, did Live Chat with Quadratec, looked at parts at a bunch of other sites and found enough pieces to the puzzle that I think I can solve it, but want to ask it again to corroborate my thoughts.
First, my 89 YJ is a rebuilt title with a mix of different models thrown in, but primarily an 89 YJ body and chassis. So using the VIN to identify the tank is a non starter.
I removed a 3" body lift along with some other restorative type projects and am reassembling everything and need fuel filler & vent hoses for the tank. It appears that the "true 15 gallon" steel tanks for 87-90 used straight diameter hoses. It also appears from what I've looked up, that they are more or less square shaped. The 15 and 20 gallon poly tanks that only differ in the depth of the vent tube into the tank to control the capacity are angled 45 degrees across the front corners and have bigger hose barbs at the fill and vent than the barbs at the gas cap fitting. Thus the special molded filler hoses for the "20 gallon only" tanks 87-95 and the molded vent hoses for 91-95.
My tank is poly and is angled 45 degrees across the front corners and has the larger hose barbs, so logic tells me that it uses the 20 gallon hoses.
But the thing that throws me is that while a 20 gallon filler hose for 87-95 is available, the vent hose is listed for just 91-95. On top of that the vent hose that came off with the removal of the body lift has the same last six digits as the 91-95 vent hose (XXX 040081 stamped on it).
Can anyone say for certain that the 20 gallon hoses are what I need for both filler and vent?