I have decided, with no consideration whatsoever for the challenge it will be, to fab up the tank with fiberglass. I will build a fiberglass tank that fits inside the envelope of the existing half tank so I cab keep mounting hardware and fittings, and I will use Caswell coating to ensure that the tank isn't eaten from the inside out.
So I sand blasted the rusty guts outta the ol' junker,
Resin and clothed the base together, leaving so fringe around the edges to help mate the sides to the base later,
AND HIGH-TAILED IT OUTTA THERE BEFORE THE FIBERGLASS MONSTER COULD GET ME!!!