I did something similar to Mike, but using the ubiquitous '2 hp HFDC' and a cyclone I made from Bill Pentz's online plans. I opened the blower's inlet to the same 9" diameter of the cyclone, and just plopped it on top. The blower's outlet was adapted to a 10" insulated flex hose and piped out the window. The cyclone's efficiency (percentage of dust removed from the stream) appears to be extremely high, as witnessed by the lack of dust on the snow in the window well after doing a lot of cutting, and by the fine wood flour in the collector bin.
An added benefit is that by opening up the blower like that, even with the added drag of the cyclone and fixed duct network, it now draws more current than it ever did with just the standard 5" to 4" wye adapter and a bit of flex hose. It'll pull 16A if I open everything, which is still not 2 hp, but then, with no motor nameplate, I can't be sure it's actually a 2 hp motor.
The catalog listing back then said it was rated for 12A at 110V, while others have said it's 16A, so who knows. But for normal operation, it draws around 12A, so it's all good.
Looking at the online catalog, they have two of them now, one green and one gray. The green says 20A, and the gray says 15A. I wonder if either have a proper motor nameplate?