Rear Shock Won't Mount to Shock Mount

it's been a while but I do remember this being a PITA even with stock components.. IIRC (and it's possible that I don't) you need to get the shock on the bottom mount about half way (so the threads can be seen but are not past the bushing) and then work on the top - (that mount should be a little loose to the inside) - a little lube will help - even just a drop of oil - then alternate between the top and bottom mount - - it'll go, it's just not the most fun you will ever have working on your car.
Compress, press, squeeze, push, even rubber mallet (on the bushings)... whatever it takes.