Yesterday, I had the same problem with there not being enough thread on the shock bolts showing to install my 5100 rear shocks and Toytec 2” lift springs. I even jacked up the axle (one side at a time), but the lower bushings didn’t compress enough to get the bolts to stick out.
Thanks to this forum, I knew to look for the washers stuck to the bottoms of the top shock mounts. Earlier today, I was able to pry the washers off and get the nuts onto both rear shocks. Years ago, I installed stock length 4600 rear shocks, and I don’t remember having any trouble installing them.
This is at least the third or fourth time I have found answers to my questions on this forum.
Thank you to everyone here who is more than happy to share their experiences/give free advice! Whenever I can, I do the same.