BlgsRX1-mtn:
You don't need a spring compressor for that. Here's what I do to compress the spring....
Take a piece of small CHAIN (not rope 'cause it'll stretch), a CHAIN BINDER, and a couple of BOLTS. Put one bolt to the end of the shock, and the other one THROUGH THE SPRING (long bolt). Hook the chain over the long bolt and onto the chain binder, then bind. It'll pull sideways, but it WILL pull back the spring. If you have two chain binders, one on each side of the spring and it'll pull straight. It does put some sideways stress against the shock, but it didn't break mine.
You might also get some observable results by removing BOTH the spring AND shock - everything should still move the same way, but you'll have to measure to where the spring *would* be.