HOW SHORT SHOULD i CUT MY REAREND DOWN TO FIT MY 10.5 TIRES WITHOUT SCRUBBING. OR WHAT KIND OR RIMS OR BACKSPACING IS AVAILABLE. iT CAME OUT OF A ROAD RUNNER SO i KNOW IT HAS TO BE CUT. i HAVE A 72 DART SWINGER. THANKS  

exactly what tires are you going to run ?  is 10.5" the tread width or section width ? What rim size to you want ? Are you mini tubbing it ?

If your cutting the rear anyways I would cut it enough so that you dont need a lot of backspacing. With the stock width a body rear you need 7.5" of backspacing to run a 10" rim. I would cit an extra 2" off the rear and run a 5.5" backspacing.  It will make it a little easier to get the rims and tires off.  I know on my 71 Dart I have to jack the car up and hang the rear to get the tires off and the are little 225-70-14s.  

I'm running a 28x10.5x15 with a 8 inch rim with a 4-1/2 back spacing hope that helps thanks  

Are you going to mini tub it ? I would cut it about a .5" shorter then stock a body width to give you a bit extra clearance at the quarter lip. You may need to trim the front corner of the quarter also. 28" tall tires get real close up front.  

I took a axle out of a plymouth and made it 3 inches shorter then my original axle i had in my 68 dart, mini tubbed it and run 275-60-R15 rear tires. Its been awhile since i ordered them but i think the back spacing was like 4 1/2 on a 8 inch rim.  

best thing to do is mount the rims and tires, stick them under the car and measure.