I managed to get the Spiralock installed, with the help of a small flat-blade screwdriver. I think it's fully in the groove, but I didn't have sense enough to measure the width of the lock before I put it in. Consequently, I can't be sure how much is actually in the groove, which is only a millimeter or so deep. A couple millimeters of the shim can be seen behind the lock. It seems secure. I can't easily pop it out of the groove with the screwdriver. I think it's okay. In fact, I'm almost sure it might be.
