[Martin64]

"I'm getting ready to restore this 1970 beast to original"

1). If it ain't broke, don't fix it.
2) The gas tank behind the seat is original, so if you're restoring to "original" than leave it where it's at.

I'm not a OEM type guy so I have no problem moving things like gas tanks around. But if you're going for a true restoration, keep it original. If it still has the build sheet on the inside of the glove box lid it will say what it was originally. If not then you pretty much have a free reign to do what you want as long as it's original type OEM stuff.

Good luck, and that is a nice looking truck.