7 1/4 rear end gear

im looking for a rear end gear for my 64 valiant i picked up a complete rear end with a suregrip but it had a 290 gear and the one in the car isnt much better would like to find a 355 or 390 new or a good used one would work

I have a 3.23 out of my 66 valiant, I haven't been able to check to see if it is a sure grip or not.