Well, the expensive bit might be on the wane now. Ordered a clone Honda Gx200 and a clone TAV. These might not be the highest quality items available "on't tinternet" but it is a start, and until proven, the whole concept should not be too powerful. More gloriously sunny grinding and fitting today.
Job one.
Finish the front upright body ready for welding and make a foolproof jig for my friend the welder.
Job two.
Make a chuck out of scrap wood to mount the big rear cog on my wood lathe to put a keyway in to match the key on the wheel face - An epic battle of high speed steel vs high carbon steel and willpower. all I can say is it worked. It might not have met health and safety requirements of a workplace, but I am not at work! (the alternative was to remove the key from the wheel with a grinder)
Job three.
Emery a few thousandths off the spacers on the Gemini hub/spindles to make a polished sliding fit into the 16mm rose joints (see CAD image earlier in this thread)
Job four.
Set out centres on carriers for drilling to accept rose joints set to a 6 degree caster.
Drink a beer in sunshine and draw spacers for turning.
Another good day.