I am running these on my '68 with a 4/7 drop. First of all you have to have the centers of the wheels bored to fit over the hubs on the 4 wheel drums. For the fronts, I am running 265/35s and have not had to do any clearancing (stock fenders and inners). I have not bottomed out or rubbed at all, but if I were to go any lower (which I plan to) I will have to do some modifications for clearance. In the rear, you can't run the stock transit because it has too much backspacing. You can either run a 1.25" to 1.5" adapter spacer like everyone above had to do, or flip the center of the wheel and change the backspacing. I changed the backspacing on mine to 4" but it did require a bit of clearancing to make it work. A more conservative backspacing would be 4.25", and with a 5" drop you should be fine and require no modifications.
