I usually install just the impeller after putting on the impeller kit. I usually have to grind down a little from each fan unless you have adjustable fans. I used to do them. Just elongated holes in rubber and nuts and bolts and just adjust up. But learned that after the fans are broke in they don't wear down anymore unless you have the habit of eating dirt and rocks.
For me anyway , the housing is much easier to install with just the impeller attached and then afterwards I can install augers.
I haven't done this on the HSS model yet. Have been turning down work on these if they are still under warranty.