Had this '72 XS tank kickin around (yes, the lizard tank). It was side side project to put it on my '80 XS. Thanks to buddy Ted, he got me 2 petcocks, a right (ended up being a left one with right side parts) one which went on here. After buying a left one and rebuilding both, it became apparent my petcocks are sort of a hodge-podge of parts. I think they are actually both left petcocks, with the right one having a right-hand lever. So the left one reads correctly, and the right one reads opposite, on is actually reserve. Anyway, I ended up having to run them backwards to fit right.
To get the tank to fit on the rear mounting post, I drilled a hole in the rear mounting bracket of the tank about 1" forward from stock. A few "unnecessary" brackets needed to be ground off the frame. I also had to notch the seam on the bottom of the tank to clear 2 engine bolts. This bit me in the ass when I had everything connected and discovered I had a pin hole leak. Some gas tank repair fixed that.
The tank was missing the gas cap lever, so I made one out of aluminum. And finally the seat had to be positioned back another inch as the tank is longer than the '80 stock tank.
Next I'm working on a front drum brake front end, different front tire, smaller headlight, and a replacement tail light.