harleyKmodel

Thanks!

Here's what I see:

1) The bung is on the left (right in the photo) side - the K-model side.
2) The bung would probably be right above the K-model carburator, hard to route a fuel line.
3) The bung does not look like a factory bung at all.
4) I can't tell from the photo if the long "dents" on the left side (right in photo) is one long dent, or two shorter ones.
5) The front mounts don't appear to have any paint on them.
6) The rear mount is a style common to fit-anything aftermarket tanks.
7) The rear mount appears to be home-attached. It's attached crookedly, and the welds are over-generous.

My guess it that Tankzilla is an aftermarket tank that has had the rear mount replaced.

Tankenstein

At first I thought it might be a rare KR tank, however given the lack of indentations on the underside and the mounts I would agree that it's likely aftermarket.