67 Dart factory fuel tank

You can see the deep recess in the tank where the side to side strap goes (it is under the filler tube in your picture). The 68-up tank has two recesses going fore and aft. There is very little slack in the straps. I would not at all be sure that you could fit the fore and aft straps over this tank, or if they would be secure without the recesses to keep the tank from sliding. You may be correct but I don't know anyone who has successfully done this — they are listed as different parts by all the vendors.