Jim, the 98- prefix was used by North American Aviation during WWII and I know it was associated with the B-25. If you see a tiny NAA stamp anywhere on the part or data tag (which at first glance looks like ANA, not NAA) that'd be a deal clincher.
The capacity has me stumped, and maybe what you have is actually a prop de-icer tank or something. I have a couple of smaller tanks from Douglas Aircraft Co. from the war years that are about 4 +/- gallon capacity that in this case held alcohol on the A-26/B-26 Invader that slung juice onto the prop to keep it from freezing and getting as aerodynamic as club.
Just a thought...
Now, keep diggin' and find me a tunnel gun mount for the Lockheed PV-2 in that cache of yours, will ya?
- Pooner