You really should have the correct tank so the straps lay in its spampings.
The pic above is a good example of where the anchors drop through slots in the spare floor. Again thats not just a 2X2 piece laying in the floor. It goes all the way across providing both of those anchors.
While we are on this subject I'll share my plan for my 67 vert.
My spare wont fit in the well anyway so I've got a space saver spare from a 94 town car along with its cover, that jack, etc, etc, to mount in the trunk.
I'm going to delete the spare tire well even raise that trunk floor area 2 inches. Then a plastic fuel tank from a 96 Cherokee fits, its straps, electric fuel pump, and all.
