Well, what I did was put the clamp around the hose and snug it up. Then I put the blade in the duct and had it run against the band. This made it fairly even, but there are still slight waves to it. I'm not sure how doing it by hand I could get it without the waves. Maybe I'll dremel them down, but that might turn out worse.
For now it fits on. I need to shorten it still, though. It's buldged out over the airbox in order to keep it off the A/C pulley:
As an aside, I had also ordered new duct clamps before the Samco stuff arrived. My original ones were rather streaky colorwise. The black was removed a fair bit from them. Oddly the new ones were unpainted. So I cleaned them with mineral spirits and painted them with the same low-gloss high-temp black I used on the oil filter. They turned out very nice, the matte black looks better than the semi-gloss finish on the originals.