First task is to trim the UHMW inboard and outboard bushings. I’m not sure what UHMW is but it’s pretty tough stuff. I used a centre punch to scribe the cut lines on the block and then used the bandsaw to gently make the cuts. I then used the vixen file and sanding block to shape them. This is where I wished I had bought a bench sander but it’s too late now and I haven’t got enough room for it anyway.
The manual says to tighten the nuts just enough to increase the turning friction of the bolts. I took this to mean that the nuts are tightened until the spanner starts to want to turn more than just enough to overcome the stiff nut friction.
The seat back hinges now need to be cut and trimmed. This was relatively straightforward with the Dremmel.
This is a good guide to identifying the right hinge from stock:
A locating hole is drilled in each.