Your going to have to find what is needed and wait for a 50% off weekend, otherwise it will cost a lot of money, just the gearing is a hundred+, it's $250.00 for what you want unless you are a toolkit member during a special, which I am not a member, so I only get a deal maybe 3 times a year, and a deal is just under $150.00, your better off finding something from a private party if one is being parted out.
Another issue you are going to have is that what you are looking for was only in the 85/86 model years.
There might be one thing that you can do, and it is a one way trip, you can pull the rear inspection cover off and see what the issue is exactly, my C200 dually rearend, which is the same as yours had a lot of play in the pinion flange, the ring and pinion gears were fine, it was the ring gear housing/carrier that was bad, well if I had wanted to, I could have turned the gears and housing so that everything was where it was supposed to be(everything aligned), and then I could have welded it up, it would be a posi then, but I was unwilling to do that myself, as it is a dually rearend.
I cannot remember if you removed the inspection cover yet, one thing I do know is that I drove mine for a long time with that clang.