I put Pinball Side Mirrors in on my Funhouse with the instructions that you simply lift the playfield all of the way up, push it to either the left or right depending on what side you're installing, and install.
It was not that easy on a system 11. The playfield does graze the mirrors and I do have scratches as a result of this and the difficult installation but you don't really notice them looking straight on at the game during gameplay. I mean, what's a Funhouse without mirrors?