Gear ratio for 7 1/4

If you are thinking of swapping in an 8.25 rear find one out of a '73-'76 A body, it will bolt in using the 8.25 u bolts and shock plates. But be aware that will change your wheel bolt pattern to 5x4.5" from your current 5x4" bolt circle , so your wheels will no longer fit. The driveshaft length will need to change by about an inch or so.
Dakota rear ends were wider than A bodies, and used a six lug axle after 1990.
Easiest upgrade is a 8.75 axle out of any '65-'72 A body, but they are pricey.
If you aren't doing any highway driving, 4.10s in your 7.25 wouldn't be ridiculous. I'm just surprised you could find them for the 7.25, and that would probably still leave you with an open rear, since most likely you've got a non-suregrip. And suregrip units for the old 7.25s are next to impossible to find. It's getting difficult to find ANY service/repair parts for the older 7.25s.