Don't know if this helps or not. I put 17 x 11's Torque Thrust 2's on the back of my '69 convert. That was after cutting the rear frame rails, moving the leaf springs inboard 4" on each side, and mini tubbing the wheel wells. I think the rims have about a 7.5" offet. Not sure about the 67's, but the largest tires I ever came across were 275's on 8.5" rims, and it was tight.
i am also trying to find out more about how wide i can get on my 69 hardtop. i will be using c4 brakes and 17'' wheels.
btw, after you mini tub'ed, were you able to use you factory rear seats. and how much of a pain was all that work?? what size tire did you use on that 17x11.??