Cheers chaps, whizzed up a tool to hold the wheels, basically a 24mm bolt cut down to hold the Heljan wheels, used high tensile steel which is a pig to cut and keep cool with HSS tools!, still it's a free and plentiful supply of steel bar, though I was tipped today by the machine shop to ask them next time as they have a scrap bin full of bar I could have
Anyway I added a small dish to take the wheel hub and then drilled and tapped to take a 4mm bolt which was then turned to 3.02mm to take the Heljan wheel. The end of the shaft was cut to a 3mm thread and a nut simply holds the wheel in place. I did think I might have to make a screw clamp on the rear but the brass is so soft and the cuts only 2 thou that the nut held the work just fine.
For the record I took 15 thou of the back and rim and then blackend (still in that process atm)
The holder
With wheel fitted and turned, the two scars on the tyre were later removed
The reason I left the large cap to the holder is so that I can ding it with a hammer, despite being turned perfectly true, once taken out and put back (exact same place as holder and chuck jaws centre punched) it can go back with a small run out, so the large end is a perfect surface for the DTI and then with a moderately tight chuck the holder is dinged with a hammer until run out is less than 0.05mm.
Having done all that its pretty much rubbish as the Heljan wheels are not round at all, well the wheel might be but the plastic insert most certainly isn't, but there's naff all y'all can do about that.
In extreme cases I loosen the chuck a fraction and DTI the rim and ding the holder until it's moderately acceptable, retighten and turn and move onto the next one.