The cylinder head has had the joint face cleaned with a diamond sharpening, block. Injector seats are recut and the valve seats tickled with a seat cutter and lapped. Thanks to Mike for the loan of tools. It's going back together with new stem seals but I pinged a valve collet - gone.
So that's another item for the shopping list (6mm three groove type).
But there's plenty to do. Piston rings will probably get done next, then I can box up the bottom end.
The copper seat washer for the problem injector was well stuck. Suitable size screwdriver don’t touch it. A tool intended for removing stripped cross head screw did the job. This is the washer, which came out flat. The top (injector) side has a clear groove where hot gas has eroded the copper. The other side has a strange wavy shape. Was it fitted faulty? Who knows.