That's correct, both the OEM plastic subframe and the 70-degree tanks are cross-linked polyethylene. Polyethylene is a notoriously difficult material to glue/seal to. That's why you usually have to use mechanical means: molded-in inserts, molded threads, or bulkhead seal plugs to fill smooth edge holes, or rubber sealed bulkhead style fittings to create a fuel tap. Quite a bit of work I would guess. I still have my OEM subframe which I am keeping as a backup for my 70-degree tank. The EOM subframe looks like it would hold quite a bit less than the 70-degree tank, but it's hard to tell accurately. Cross-linked polyethylene and polyethylene in general can easily handle any type of fuel (gasoline, ethanol, diesel...), that's why they make gas cans out of it.