So here is my attempt to fix the buckled side.
What i did was after sanding the outside edge of a block to fit as a caul and clamp that against small block on the inside edge. Before the clamping I added some water to the area needing to be modified a small amount at a time and then used a heat gun on the area and tried to get the clamp on as soon as possible after taking the heat away.
I left the clamp on about 15-20 minutes the first time, and then repeated the process and left the clamp on overnight, i'll see how its done tomorrow. The first attempt took it pretty close to "normal" still not perfect but at least not obvious. Even after the overnight clamping, its unlikely to be absolutely perfect, but it should be much improved and hopefully "good enough"
While waiting for the clamping to take effect the first time I made some headstock routing templates. Two are my own design, and the same shape but one is slotted, one is flat. The third is the "traditional" slot head design that came with the plans I bought. I really like my own slot head design, but i'm leaning towards my standard flat one for this guitar. Ive left the edges of the template deliberately slightly oversized so I can have a very slightly wider neck at the nut if I decide not to go for the typical 43mm and just carve down the small difference with a file/sander/sandpaper if I go with the 43mm
clamping the side "straight" seen from the outside with a shaped caul
Untitled by
David Emm, on Flickr
the inside used a straight caul as it was just to give a vertical surface to clamp against from the other side
Untitled by
David Emm, on Flickr
Headstock templates
Untitled by
David Emm, on Flickr