@Shauki inspired me to not quite be so freekin paranoid and just build. So I turned some spacers to hold the bed. Turned out pretty well, so far, and will make bed changes a breeze.
Next lesson learned: Round things SPIN. 
Nothing some additional tape didn’t fix.
@Shauki is inspiring, as he has the M/m=1/$ with the ‘try it now’ attitude. The Mind/material success he has puts the ‘weldeneers’ I work with to shame !
Good idea! If you drill the hole off center you will be able to grip different diameters and snug them nicely.
I had been using spring clamps to hold the plate down. They smell bad when the extruder sweeps past. They scare the crap out of you when they jump off the plate (and ruin the print), and kept me from using those pressure sensitive sensors I currently have on order. The math called for 26mm disks. I made a 26mm one and two 27mm disks and things are quite firm. I’ll grind facets into the larger disks if I need to in the future, but I’m not sure that’ll be necessary. The spinning took me by surprise initially.
I’ve got extrusions, it seems like the design takes a LOT of roller bearings, though. There’s a tradeoff, I was investigating using 12mm and 8mm ground rod and turning bushings out of Delrin…vs using extrusions and a TON of roller bearings.
The cheap ones have a high initial reject rate (I managed to find 6 good ones, but it took two orders of 10 to get there.) they also don’t support a rotating shaft like the Ingentis. You’d use something like this: http://www.rakuten.com/prod/12mm-stroke-rotary-ball-bushing-12x23x32-linear-motion-bearings-vxb/229168340.html?listingId=302733697&scid=pla_google_VXBBearing&adid=18179&gclid=CM36n_6-v70CFeMF7Aod3X0AGQ
Bearingins in the quadrap: weren’t there roughly 20? (3 per carrage, times 4, plus 8 in the ‘effector’?)…adjusting the preload so there wasn’t slop seemed like it would be hard to do, and relyant on the extrusion frame being completely square and true.
The Ingentis design allowed for the adjustment of the ground rod endpoints to be adjusted, even if the extrusions weren’t quite square. (forgive me if I’m missing something obvous, I’m still concentrating on my Delta and haven’t started work on my ‘big cube cartesian printer’ yet.)
Oh, I have VERY mixed feelings on the Delta. I’m sure a large portion of it is based on my lack of experience, but they’re definitely finicky, and have their own limitations and quirks.