When I did mine I had a Unimat 3 at the time but the faceplate was slotted for tee nuts so no problem with the studs.
One way to do it with your faceplate would be to get a scrap of say 6mm plate, trim to approx circle and bolt to the faceplate using the existing slots. Then tap 3 equally spaced holes say M6 to take bolts/studs nearer the center and use these to hold the flywheel.
If using the 3 or 4 jaw reverse the jaws so you are gripping the inside of the rim, trying to do it holding the ctr boss won't be rigid enough.
I agree with message above but if held on faceplate, which I think is best method, hold securely but do not over tighten bolts over spokes as they will bend/flex etc. Use packing beneath spokes to take the strain if needed, but still allow rim to rest on faceplate and take majority of pressure. Machine flywheel face, edge, boss (plus bore, not drill, hole for axle) all in one operation. That way you will get a perfectly aligned flywheel with no wobble. If you find using the faceplate isn't achievable, then as above again, reverse jaws and hold on inside of flywheel but do not try holding by the boss.
I did the 10v a few years ago,and using the face plate is the way to go. As Jason says use a serperate sub plate fitted to the faceplate. It will come in handy for lots of jobs and you will be able to drill and tap into it to suit for each job. Then when its riddeled with holes, just chuck it away and make a new one.