i did a complete frame-off on my 51 3100, but I did by a new replacement gas tank from one of the usual suspects we all use. No issues with it, no fumes, etc., since I finished it in 2019. And my battery is in the stock location under the passenger side floorboard, and no issues with that either.
I figured the folks who designed it, knew better than me, (there you go HRL).
