The drift cutters on my blower are about 18" above the deck. The taller you make them, the stronger the material you'll need. They need to be strong in both directions (forward/back and side to side), mine are stamped out of steel so they have strength sideways but still act like a knife to get through the snow. If I were making them from scratch, and I lived where you do, I'd probably use rectangular tubing that's about 1" wide by 2" deep with 1/8" wall. That would be easy to bolt on if you don't want to weld and has enough wall thickness to take a pretty good load. You can buy drift cutters for walk behind snow blowers, but I've not seen anything that would work on the size machine you have and the kind of snow you guys get up there.