Axle Swap??

I'm fairly new to Mopar, please bear with me.

I have a 65 Dart GT with a 273 V8, 904 auto, with a 7.25 diff 2.93:1 ratio.

The diff needs an overhaul, and I figure this would be a good time to go from open to limited slip. A Shure-grip,(Powr-Lok?) is impossible to find at least for this diff. I've run across some other Mopar enthusiasts who recommended that the 7.25 diff is a little weak for the V8 package; that I would be better off with an 8.25 or bigger. The wheel ends are 5 on 4. I'd like to try to stay with that as I have Cragar mags, I don't really want to lay out more cash for new mags and front and rear will have to match to boot.

What should I look for when I go axle shopping? Year? Model? type of thing or where axle options for the Dart varied?

Here's a picture:

Thank you to all.