Well I was also with the first one I did! I set out a clean white towel on the table and then made up "spanners" from wood dowel and hacksaw blades to fit the various internal rings with notches. Just took my time making the little tools, and carefully laid it out where it could sit for the time it took to get metal parts finished.
Once the parts were done I simply reinstalled them as they were laid out on my towel and it worked. It's a bit daunting until you do it, and then it made me wonder why I was worried.
