I've got an '85 tall rig bow sprit and have had to do the replacement of the compression block in the bilge due to rot and it was no easy task to be sure, including unstepping the mast, lots of drilling a chisling of rotton wood and then the fitting and epoxying of the new block. Very labor intensive.
I have never heard of compression post problems in boats of this vintage (seperate from the compression block issue) and my post is basically a teak box made up of four pieces of teak screwed together. I have seen many other types boats though where the compression post was a stainless steel tube though, maybe the later Catalina 30s have converted over to this? What's your compression post made of MortyD?
I would agree that if you need to replace the compression post it should be a fairly easy task with the mast down. The compression block... well... that's a whole 'nother story!
DanM.