Ok, so I've been chatting to Mikke, and this is what he said about the willow bow that he made:
"It was an experiment that should not have perform so damn well. If he want's the willow to get as strong as possible it's good to leave the bow's width a little more than usual.
No has heat treatment on the belly. But it would definitely be good to get more lb.
The bow is 202cm and last pull was 86lb at 32½" total sett was only 6cm."
The dimensions are 36mm wide and 33mm deep in the centre, with an even taper n both width and depth towards 14mm tips.
I'd say go ahead and use willow to make a bow. The worst that can happen is that you don't end up with a bow, and the best that can happen is you become something of an expert in a bow wood that many consider pointless. Mikke was certainly very happy with it, and that's a guy who really, REALLY knows his obscure bow woods.