All Right! Went out this a.m. and cut the vent for the air return into the shop. Also installed the 20 inch filter holding grille. Looks very nice, well sealed/tight fit. The opening is smaller than the grille, but plenty large enough to replenish the air. Have a little more sealing to do, and to shorten the hose into the SDD, but basically it's done except for a little work on trim, plugging air leaks, holding down the linoleum at the entry ways, and eventually, paint.
The picture shows the SDD, top of the chip collector, the HF DC unit and in the upper right, the vent, covered by the white grille. Set the grille up so I can change filters without having to move everything.
The more I do, the less I accomplish.