[gearhed1971]

I have a '63 falcon with a '68 mustang rear end in it, and I'm trying to find the correct tire/wheel combo for it.I would like to go as wide in the the rear as I can,but 225/14/70's won't fit. I have tried ranger wheels and American racing universal 7" wheels,but there is 0 clearance between the tire sidewall and the fender.

 

[Cuda_jim]

Sorry I don't have the definitive answer but.....Once you determine how much room you have you can decide on the tire size.
You'll need to do some measuring of the wheel wells and distance from hub to hub. Then a little research on the tires....rim width requirements and girth (widest point at the side wall)
Then you'll need to determine the rims back space.

Take a look here:
How To Measure For Proper Wheel Sizes

and here:

http://blog.tirerack.com/blog/ethans-tire-and-wheel-news/0/0/whats-the-biggest-tire-that-will-fit