They are painful, but worth it.
The cleanup is best done over several sessions, I do mine on weeknights after work when you only get 1/2 an hour here and there.
For the assembly, I made a Jig out of a few peices of metal that I got from a hardware store each had 2 screw hole offcentred ( they look like a door hinge without the hinge if you understand it) I've got 4 screwed to a peice of 4 x 2 about 300mm long. One side is screwed permanently to the wood. The other side I made different size track links and screwed the metal so it can be moved for each type of track.
After all the cleanup has been done on the track links, I lay them out in about fifteen per time and drop a hint of glue on them and the holding the links firmly in the jig with a metal ruler I use a set of twisers to push the links together.
It's actually easier to do than to write about!!!!
Gaz