Hey Zach,
Fred sounds like he's got you covered on most of those points. Additional comments...
1) I just went and put an S70 NA clutch (228mm) in a dished flywheel, and it fits perfectly. My housemate's 740 (dished flywheel, M90 diesel plate) now runs a ClutchNet 850 (228mm) disc, and it works very nicely...very streetable. As long as that 850R clutch is 228mm diameter, you should be AOK. Were the 228mm FWD clutches always for a solid flywheel? If so, they should have a sprung centre, while the dual mass ones have a solid centre. You may need to make more or less of a leap of faith on this one, unless we can find someone actually running an 850R disc.
The other thing to bear in mind is that we got an M90 diesel clutch (complete) to hold around 300lbft before it started slipping. Quite independently, a clutch specialist said that the limit for a 228mm organic clutch will be around 300lbft. Unless the 850R disc friction material is made of something exotic, it may be no grippier than an M90 diesel disc, and any 'magic' is all in the 850R pressure plate...which won't fit the redblock dished flywheel. On that basis, I'd be sorely tempted to fit an M46 turbo plate with either a lesser 850 disc (if they're cheaper), a M90 diesel disc, or even a ClutchNet 228mm sprung 4-puck. The one in Ryan's car is very "streetable", given what it is.
2 and 3) I always align clutches just using a 3/8" extension bar. When it "wobbles" an equal distance up, down, left and right (pivoted from the pilot bearing), the disc is sitting centrally. The car I just did had an M46-style pilot bearing in place, which clears the M90 input shaft fine. The metal piece you've pictured there is only used for clutch alignment - the input shaft doesn't make contact with it (obviously, if you think about it
). If you already have an M46-style pilot bearing, I'd use that to align the clutch. If not, the PN for that metal jobbie appears to be 1397077...but that's all it's there for: clutch alignment.
6) The bracket you have is the same one in the Vadis pic...it's just a crappy drawing of it. You can either bolt it up to the underside of the shifter boot clamp bolts (once installed...using 10mm-headed (M5? whatever...) nuts), or slip it over the edge of the opening in the chassis before you bolt the shifter boot down. The latter is the stock setup, but it does make removal more difficult.
cheers
James