I used a hose clamp so I could scribe a good circle around the pipe. Some of it I
cut off with a cut-off wheel, chop saw, and a hand held pipe cutter because I was
working late and didn't want to make a lot of noise for the neighbors. 
I cut out the notches in the end with a thin 3" 3M cut-off wheel.

I used a magnet and level to line them up.

Buster is helping out.

You can see the welding mask inside the supplied air hood and the arrows and the little dots.
I cut two slots in the supplied air hood in the upper and lower part of the face shield
with a pair of scissors and utility knife.
Then I aligned the helmet with the face shield and put masking tape on the edge of the
face shield and helmet to hold them together, and it worked really slick. You can see
some masking tape on the lower part of the hood, I have used this hood a lot and I 
tore it, so I put masking tape on the hole and it's been holding for a long time. I
can't say enough about the supplied air and this type of hood. They are a pleasure
to work with.
To repeat here,
DO NOT WELD OR GRIND WITH A PAPER SUPPLIED AIR HOOD BECAUSE OF THE FIRE HAZARD.