The tank is nice. Are you going to use the side to side strap like the car came with, or switch to front to back straps to hold the tank in? On my 65 Barracuda, I'm going to switch to the later type straps to gain some room for dual tail pipes. There won't be much to making the mounts.
I did that on my 67. I used the trunk piece from a 72 dart and modified the cross member for the other end. I'm a little worried about the integrity of the cross member part. I am trying to figure out a way to reinforce that area.