Your Mark was manufactured as a Mark 5/V. When SS introduced the Model 510 they started calling everything before that a Model 500, so that is what yours is. We sometimes use "pre-500" and other terms to differentiate among the 500's. Looking at the carriage in your second picture, yours has not been upgraded and remains a 500.
Models 500, 505, 510, and 520 differences are the table systems. The later models have larger tables and the ability to expand the table system. All for a price, of course.
SS used to have pdf summary manuals for all models for free download, but looking at the site I can no longer find free versions. Here is a Mark 4 manual: (
https://shopsmith.com/wp-content/uploads/857400-FREE.pdf) Primary differences from what you have is the machine is shorter (shorter bench and way tubes) and it has a 520 main table. They have the 500 manual for purchase, but it is paper. Maybe another member knows what's going on with the pdf manuals.
- David