You can also slot them and when you have the right position, drill a #30 hole in the center and install a SS pop rivet to eliminate any vertical movement. On my 6, I slotted them (about 1/16" of movement available). I figured I would put the rivet in when done testing. I never got around to that and 600 hours later (checking for movement on every pre-flight) it hasn't moved. I figured the worst that could happen was it would slide into it's old position, which was perfectly safe.
Larry