It sounds like a fun and doable winter project, so what the heck. A leaner sidecar attaches to two points across the bike longitudinal axis, the front being higher so that the car itself will turn a bit while leaning.
So far so good - it appears that I can mount a brace with a ball joint/bearing on the upper two bolts that hold the frame's sections in front of the engine.
But what about the rear mount ? The cross section bellow the engine could work but I have some doubts about adding stuff beneath a stressed engine/gearbox assembly.
Hack fans, please do tell :)