One of the interesting things about the factory part drawings for the Sheridan A is that there are no revisions notes or changes to any of the parts. Either the Super Grade never changed during it's production life or they just weren't very good at keeping the part drawings updated. The one exception is part A508 the Sealed Unit Retaining Nut. This is the nut that has to be removed before the Sealed Unit Assembly can be removed.
Here's the original model A508 version:
Here's the second version, part AB508:
For anyone wanting to remove the Sealed Unit Assembly from their Model A/B, you're going to have to make the special tool to remove this nut. The outline at the bottom of drawing AB508 gives the basic dimensions for making this tool. The Sealed Unit Assy projects out far enough that this tool needs to be 2-1/2" deep to make clearance.