When the seatback frame components had well and truly cured I cleaned everything up and levelled the sheerclamp and upper stringer so that it is flat across all along its length.
I found that the Shinto saw rasp was very good at quickly roughing the top of the seatback to shape, working back and forth across it, and the block plane and a good chisel were great for smoothing and trimming.
I think this is the first time my 'best' chisels have featured here. They are made by Blue Spruce, and are superb. I reserve them for 'proper' woodworking activity. My old chisels are fine for hacking epoxy resin and plywood.
Here is the port side being levelled out.
And here is the view of the port side, looking forwards.
A final pass over everything with the finishing sander and it looked good!
We are getting there ...