I know I put posi in the title but, I am doing a 10 bolt Chevy. I think my solutions would work on Mopar C-clip rears also. It can be a bear to install the clutch packs and keep them in place while installing the spring/thrust plates. I brazed a 1/4" nut to a 1 1/2" fender washer and used 1/4x3" bolts to keep the packs in place. The washers fit in the C-clip recess (nuts facing out), bolt sizes as applicable to the unit. I then compressed the springs/thrust plate assy in a vise and put more 1/4" bolts and nuts in the wide end of the assy. By squeezing the narrow end of the plates together it slid right into the differential far enough to remove the nuts and bolts and then continued insertion. Once in place, I removed the fender washers and then placed the spyder gears into position-piece of cake!
Mike
Mike