Recently, well a few weeks ago, maybe fifteen years ago I did dust collection in my shop. I used light weight (SD) plastic pipe for the ducts, 6" and 4". That boot you showed is an "end" boot. I too have a contractors saw. I made a sheet metal box similar to a cereal box and it slips up from the bottom around the blade and the lower end terminates into an end boot. It points toward the operator side and there is a blast gate with a micro switch that turns on the DC. The gate is beside the switch for the saw. The top of the box is cut off at a forty five to allow for a full tilt. There is a loose lid that closes off the top except for about a 1/2 slot for the blade. Does not sound like much, but a lot of thinking with into it. I don't have an over the blade collector. The way I can tell the DC is not on is sawdust hits me in the face.
I also started with a 1 1/2 HP Delta DC.
I suspect if you had a DC powerful enough to suck the carbide teeth off a Forrest WWII Combo blade the set up could be even simpler.