The long overflow tank is available reconditioned from Larry Stock's www.PanteraParts.com in NV. I think its bracket bolts to the upper right subframe, visible if you remove the engine screen & rt side piece. I removed mine so long ago, I can't remember if I cut it or just unbolted it!
By cutting the weld that holds the short swirl tank bracket to the inner fender, you can remove it for work as necessary- the rubber linings deteriorate and lets both tanks move around to rattle To replace the swirl tank bracket, simply drill a hole or two and use sheet metal screws to hold it. .When you do this, re-rout the A/C hoses and reposition the tank & bracket closer to the right-side decklid shock. This makes it easier to access #4 sparkplug.