Looking at the PA inspection manual it says:
Reject if:
A fuel tank or line intrudes into a driver, passenger, or cargo compartment except if vehicle was originally so designed.(aka the 69-72 pickups with the tank inside the cab)
Your state? damned if I know, but its technically illegal in mine.
Hell if I really want to go letter of the law, strictly how it is written, puting a fuel cell in the truck of our 69 Firebird is illegal.