For sure I chamfered the lowering edge and bowed the galley flat to get it in , forcing it with light hand on rubber mallet when scraping against wires. In the end the fillet covers up the deformations. No issues in the end but it was the worst fitting of the project.
my experience was about 3 months ago, so my memory is a bit foggy. when I first tried to install the flat, I thought it was just plain-ol too wide. so I took about 1/8 inch off each outside edge of the flat. it was still a tight fit, but after several tries, putting it in at different angles, it finally dropped right into place. then I discovered that I had trimmed off too much, but a thick bead of epoxy putty on top and bottom of both edge joints covered up the slot caused by the excess trimming.
because of the way the sides of the hull are angled, I think there is just one “magic angle” that you need to position the flat in, relative to the floor of your workshop, at which it slides right in without much force being applied.
if you can’t find any angle at which it slides in, get out your block plane and shave a little bit off each outside edge and try again.
For what its worth, the galley flat is in. I’m happy with the solution in the end, I agonised over it and put it off for a week or two, but in the end you just have to make it happen. My intended solution was to round the sides to make it easier to get in and take a sixteenth of an inch off both sides. It might have worked but I ended up taking an eighth of an inch off instead and then trying it. A Solution? The flat went in easily enough but I had maybe a quarter of an inch gap either side which I didnt fancy filling in with a fillet, so I used some 3/4″ quad, and it works and wont show since its underneath. Have now moved on.
there definitely must be one and only one “magic angle” at which to insert the flat so no trimming is needed. my experience was the same as yours–took 1/8 off each edge and ended up with gaps. I filleted top and bottom and after a few thousand miles, no issues.