Great rock find Sis. Looks like it will drain well. I have just the semps for that wonderful petrified clog.
S. speciosum, it stays tiny.
Or this sweet little S. 'Pixie'. It gets a tiny bit bigger than speciosum.
Or this awesome colored (in spring) S. comollii. The largest rosette is 2 1/2 inches across. Maybe not meant for your clog rock. But I'm sure you can find something else to put it in.
This is another nice small one. S. 'Hookerii'.
And I mustn't forget Silver Baby and Silver Angel (her spring color). Both tiny semps.