They only charge you extra for the hammer block and magazine catch PARTS, but they come already INSTALLED in the grip. It's about $6 more, but the only way to go. You NEVER want to pull the shiny hammer block pin unless you HAVE to.
After you remove the slide, protect the frame and pull the trigger. That will remove the tension from the hammer spring so you won't over-stretch it while disconnecting it.
To put the frame into the grip, you have to push back the hammer block from behind with something thin.
Packer.