2" will be fine. as Blue said.
if you have a tig and the correct bends, then go for it.
when putting a hole through your guard, you may want to look for a sheet metal shop that has a hand held punch to punch out the hole instead of a hole saw, which in the wrong hands can end up very messy.....
we have a few little units at my work with punches ranging from 22-90 odd mm in dia. much cleaner hole, a lot less work.
