Thanks guys. I had found that site but with few and small photos its not great for getting details.
You are right, it looks like maybe some spacers in there, and a sort of tophat washer to plug the dropout. Seems a bit faffy given they have gone to the bother of machining something for it not to fit. Guess its just too hard / too much work for them.
Measurements shouldn't be too hard to work out....
Dropout is what, 9/10mm across and maybe 4-5mm deep, and the skewer is about 3 (I have a ruler, I'm just guessing at this point), so getting something machined to fill the gap with a fairly flat top to hold against the side shouldn't be too hard (he says, with no machining experience or equipment). I suppose a spacer here will hang on the qr and slot into the frame, rather than fixed to anything. But for what purpose? In my head it needs some mechanism to extend the axle not just fill the gap.
The 'outside' has a recess for the head of the skewer so it should stay seated but I can't see that adding much to the strength of the whole thing. In my head it needs to be held firmly in place to resist the turning applied by the brake. If the bracket twists the pads move out of alignment with the rotor and that could be rather bad. I'm reluctant to drill a hole and fix the adapter directly to the frame but that's what the bumpf says so maybe that's what is needed. Again, seems a bit cack to me.
Spacers for the caliper - guess they are readily available for other applications, just need to make sure its ID is sufficient for the bolts. Ill hit the hardware store / ebay later and see what I find.
Does anyone have one of these who can shed more light?