whoa I keep doign that.
the ones for sale are 170 MM arms.
I also have 175 MM arm withOUT a chainring. You will need longer chainring bolts due to a boo boo (they weren't fully tight from the shop) that caused the ring to coem off. So the initial teeth to screw the rings in are soft, but with a longer bolt they can be done. I am selling that one for $60