Here's a pic of the 5222 installed in one of my testing heads: to show the needed clearance between the slide ring and the valve stem tip.

If the slide ring clears the valve stem tip, I will be able to get the correct valve lash clearance when I install the lifter bucket and adjustment shim.

The SOHC slide ring is ~2.004in diameter. The same ring is used on all the redblock SOHC heads. The stamping of "B21" on the ring merely indicates that that ring is for the SOHC, rather than the larger ring that comes with the tool kit which is for the D20/D24 diesel motors.