Mopar Mistake 'Not offering a 273 Commando HP II 'option'
It's not that the tank is offset, it's that the 67 side-to-side strap has the J-bolt only on one side, and it sticks out into the space the tailpipe would occupy.
I installed duals with 2.25" pipe from the mufflers back, and I just slipped some gas hose over the threads to keep it from banging against the tailpipe. But that's not something the factory would do.