Please tell me what parts interchange between the 2.45/2.25 vice 2.71->up 8 1/4 axle

What exactly was wrong with the kit Roy posted that had everything in it? Are you like me and have to buy it one piece at a time? If so, I get it.
And I’m kinda poor haha I skimp where I can , I maybe going this route now and might cost more then the 8.8 but unsure until I see if I can find a sure grip or whatever they call the newer ones haha. Like I said mopars are hard to find parts for here in central ca.