Thanks for posting, Richard! For a stamp of 27C, I think you should choose the 2730 option. Some companies use letters for the stamp instead of numbers. Traditionally A corresponds to 1, B to 2, C to 3, etc.
Do they just pop out with a screw-driver? I've tried to remove it from an intact window and it's not coming out easily.
Richard
It should be screwed in. Keep in mind that you will have to remove the sash in order to remove the top sash guide.