Yes Fred, hydraulic cylinder pushes the whole plate with half coupling forward to disengage then rotates and clamps once there.
You obviously need some means of having the shaft move without the motor or pulley or whatever also moving. On my first turret I had a splined section in the middle of the shaft and the pulley was splined. On this one I have a splined section of shaft bolted onto the end of the shaft and use a splined bush on the end of the gearbox.
The gearbox is planetary box, so inline, with a 25:1 reduction. That way I can use a smallish servo to rotate it.
Hood