So it looks like a year has passed and this project has been moving along and nearing the end of concrete work.  All the walls have been formed and poured and all that remains to pour is a final section of slab so focus has been on finalizing the underground work in that area.

I ended up buying a bunch of the metal inlet boxes that Hasbeen found (THANK YOU!): [Link: builtinvacuum.com]

They weren't designed to work with a powered SuperValve and were setup for the pipe to come out of the top, so I had to cut & grind them up and combine 2 boxes to make one and then sort out fittings for high & low voltage using liquatite and then fit 2" sch 40 PVC to the back to be used as a sleeve for the central vac pipe.

Looks like it's going to work out.  I fit the inlet last week, but trim out won't be for another 12-18 months.  Here's a few photos...