What can a 7 1/4 rear take???

There is a formula to do this, mark your drive shaft and wheel, tune the drive shaft and count how many times the drive shaft turn to one complete rotation of your wheel.
Do you have the build sheet to your car ? it will be on it if now one changed the gears out.
A good tec can and will jump in here and tell you what you have once you find out
how many turns it took to do one revolution of your tire.