A Mickey Thompson 295 55 15 drag radial under a 68 GTX, 15 x 8 4.5 bs, stock suspension 8 3/4. I took some measurements & looks like it will fit. But I would rather a confirmation by someone who has tried it before I spend the money. Many Thanks, Danny

that should be fine tire is 12" wide at the center section (widest part ) so on an 8 " rim 2" inside and outside of rim so 4.5 + 2" is 6.5 inches from the flat/face of your brake drum and on my GTX there was about 7 7.5 inches from there back to the spring you can measure that.
the 8" rims may suck the side wall thus the center section in a bit.

My old slicks had a 14" center section and 4.5 back space 10" so also 6.5 inches and I has fine on spring clearance.

You should be fine on the outer side with a 8 inch rim but measure 3.5 inches + 2 " = 5.5 inches out from drum mounting face.

Thanks dodgem, I was looking to fill the wheel well & this tire should do it.

68 GTX's look good with a meaty tire!