Ed, from the photo description I thought you may have attended Purdue. I spent a few years there.
<<The Mark V/5 was preceded by the only slightly compatible Model 10, and followed by the largely compatible Mark VII which had a few unique features. Next Model 500>>
Model10, followed by Mark VII, followed by Mark 5, followed by Mark V, followed by Mark VII. Arabic, followed by Roman, followed by Arabic, followed by Roman, followed by Roman.

Russ, confusing it is.
<<the original Mark V became the Mark V 500.>>
Are you saying the original Mark 5 became the Mark V 500?
<<A clutched Gilmer Drive Sleeve Assembly had replaced the non-clutched one.>>
Can you explain the difference between the clutched vs non-clutched version?
Here is what I think, I have a Mark 5, is says so on the name plate.

Thank you both for helping me understand the sequence of the models.
Paul