Dave,
I don't think it is as hard as you are making it- but then again, I didn't take the bolt out that holds the upper block either (but, to a certain extent, if that ain't specifically broke, then you don't need to fix it). Some people have recommended taping a line to the bolt as you pull it out, therefore giving you the ability to pull the blocks out but still have the line attached so you can thread it again. You can pull out the rest of the innards and look at it being mindful of how it lays when put back in. The blocks themselves are protected from everything- nice a cozy inside the mast- so they have no real reason to have an issue even with the high loads they see. Onviously a good spray up in there every once in a while is good to remove salt, etc though.
once you remove the base you will be able to see how the purchase is set up.

and for the sewing- one pass in each line with whipping twine, square knotted a couple times... taped with electrical tape is all you need. just be gentle and there is no reason why it shouldn't work. I have done this about 5 times in replacing/trying different downhaul line and works fine. just do it man!!! <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />