8 3/4 help

As of right now the 8 3/4 rear end is a one wheel peel. The 71 Demon it is on had been stting for like 20yrs. I just got it back on the road last year after installing a front disc brake conversion along with new suspension upgrades. It now has 5x4.5 bolt pattern on the front but 5x4 in the rear.
I would like to put a sure grip setup on it along with new axles with the bigger bolt pattern.
I would than install a rear disc brake conversion also and possbibly change the rear gear from 3.91 to 3.73 or 3.55.
What are my options without breaking the bank. I have been looking at Dr. Diff parts, heard many good things.
Can anyone point me in the right direction? I'm really not sure what all i need, like bearings, shims or install kits etc.
What do i need to make the rear "posi"

Thanks
View attachment 1715909465
I run a spool on my Cuda. It is not street friendly, it is designed to go fast in straight line and not turn. As so many have already pointed out call Dr Diff and tell them exactly what you have and exactly what you want.