Thanks, all. Well, I figured out my drawing above was a little different from the real thing...so here is the revised version:
First I removed the impeller inlet and bought twelve longer (metric) screws to be able to screw through part #1, and attached the impeller inlet back on, along with part #1. I had to mark and cut clearance in part #1 for the exhaust port. I then attached part #2 to this assembly using wood screws, facing the groove side down. By the way, I used foam weatherstripping in all the grooves (you'll see them in parts 1-3) to help seal against the collector and the chip can. I attached parts 3 and 4 together, with the grooves facing outward, as well.
Then the 3-4 assembly was put on top of the chip can, the collector was placed on top of that, and the impeller assembly on top of that. The I used threaded rods and nuts (think it was 5/16 inch dia), in four places to trap the collector into place and provide a good seal. Gravity provides the seal against the chip can. I used the transparent (and expensive) 4 inch hose from Woodcraft USA for all the connections. At the hose ends I used hose ends from Woodcraft also, which I fitted into PVC adapters. Also being a bit paranoid, I ran some solid copper into the hose at each end and grounded it to my router mount at one end and the impeller assembly at the other. The eyebolts were added to provide a way to hoist the motor/impeller assembly up when the can needs emptying.