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Not a great diagram but hopefully it makes sense. The exhaust clamps aka u bolt clamps can be tightened onto the frame more tightly than fragile tank studs, too.
If you need extra space for the petcock I think you could raise the tank further by adding a nut or two to it's studs above the plate. This would also mean that the nuts securing the tank to the plate would be tightened together, pinching the plate, so they wouldn't stress the fragile welds.
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