After laying out the parts in CAD it has become quite clear that with a bit of clever measuring the necessary accuracy is rather easy to achieve. In reality the actual foot-support would only need four holes in the right spot and right in this case only means symmetric, which as long as you machine both parts at the same time, is rather easy to achieve.
A set of adaptors was also necessary.
In order to interface with the mounts on the footpeg-frames, a square had to be milled onto the back. (30x30x5mm is a good start, if you have similar ideas...)
As the astute amongst my dear readers will notice: there's only 3 (through-)holes, the 4th is just 5mm deep and meant for a press-fit button, so that the button takes all the weight and not the bolts.
Considering the fact, that I use M8-bolts, it is absolutely unnecessary, but it's the sort of engineering mindfulness that gives me those warm fuzzy feelings... 😊
The finished product.
Doesn't look like much from above - but it's a full 10cm (4") further forward.
Hold on a second, what's the point with these pictures? Simple, I built the forwards and realised I have to completely revise them, so I converted the bike back to almost the starting point - the handlebar-raisers (25mm) are still in place.
So was it a complete failure? No, not at all. 130-140mm are about where I want to end up. The whole setup was too wide, i.e. I couldn't adjust the rear footbrake the way I wanted it and even after shortening shift lever twice, I still couldn't reach it even half decently (hence the controls would have to be moved even further forward), yet further shortening would definitely not be possible as the gearchanges were already a bit stiff. (Very precise though) As a sidenote: the new setup will be made from stainless allowing me to dramatically cut back on the thickness of all the plates. It will be an absolute nightmare to machine though.