Everyone says don't remove the spacebar because it breaks something on a Model F but no one ever says what breaks?!
I have never broken one, but it is a monumental PITA to get back together because there is an entire "under-carriage" assembly that goes on the back side of the plate. All the pieces have to be in place as you snap it back in place.
I found that using a weighted thread (such as a screwdriver on a loop of thread hanging over the edge of the table) to hold down some pieces while I use my hands on others works well enough. I have not done one of these in at least 2-3 years, so I don't remember the particulars.