72 skylark rear axle posi installation..Help needed

Need help with my installation..i got a 91 caprice posi rear end it looks like it has the 30 spline shafts..it is a 10 bolt 8.5....i wanted to install the differential on My Buick SKylark with a 10 bolt 8.5 28 spline shaft....would this be possible..a month ago i was told it was.. Is there any difference in the shafts...let me know you can also email directly for faster response to al72gs5063@sbcglobal.net..thanks

Caprice vs Skylark, number one are the axles the same length, I don't think so.

They look very much the same from the outside, the only difference is the strut mounts and the bolt pattern..everything else looks the same.. as far as the shafts themselves..i will try to open my 72 buicks rear end and try them...im guessing as long as the diameter of the shaft is the same, everything should bolt up pretty good.. unless im missing something...else..