Re: Reclaimed from the junkyard!
Unless you're intent on using that petcock, you can replace it with a 90 or a 45 degree fitting and go with an in-line valve instead. Do you really need a 'reserve' position?
As for your idea for the rear mount, instead of just a screw into the top tube you could install a Riv-Nut. They should be available at most industrial tool suppliers. I typically use only a 10-32 Riv-Nut on the rear mounts for my tanks. If the front mount is strong the rear one just keeps the tank from bouncing.
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