I have to always take a few moments to once again oooh and ahhh that beautiful Slingerland kit of yours, Steven. I'm a Yamaha fan, too, but there is simply a deep, classic beauty in White Marine Pearl wrap.
This was my experience too with a 60's Ludwig kit. No matter how much I tightened the thing, the cymbal and stand would fall. A friend of mine in those days had a telescope cymbal stand coming out of his bass drum. This didn't offer many positioning options, but it seemed to hold better.My first set, a four piece Slingerland built in the late 50's, came with a bass drum mount for the ride cymbal, and I hated it. I would tighten it as much as I could, but that mount had a bad tendency to slip, whereupon my 22" ride would wind slowly fall toward the floor. There's even a video from that period of Gene Krupa soloing on national television as his ride takes a dive. The first alteration I made to those Slingerlands was to get stands for my two cymbals (it had a second bass mount for the 17" crash).
Maybe the modern mounts are more stable, but I'll pass.
I do note that most of you who use them seem to set them up so the arm is straight up. My setup required the arm to be at an angle, which puts more strain on the mount.