Before something like the 1950s, casting techniques created a much rougher pan that fundamentally required grinding of the surfaces to make a usable cook surface. New(er) casting techniques developed that had a much tighter sand-pack for the casting mold, plus some sand blasting after the mold, made for a faster production cycle, but at the cost of leaving a slightly pebbly surface on the pan.

Because the older techniques weren't close to usable after the casting, the cleanup process made for a smoother pan. Because the newer techniques were much closer to usable after the mold, less cleanup was put into them, resulting in a rougher pan.

A cheap angle grinder is good enough for the relatively soft iron alloy used in cast iron pans. Grind the surface down smooth (don't forget to wear a face mask!), then finish up with increasing grades of sandpaper until you get a nearly mirror surface on the pan. Season the pan a couple of times and you'll be left with one of the most durable, non-stick surfaces for cooking that you can possibly have.

I think even without the angle grinder it wouldn't take much work starting at 220 by hand. use vegetable or food safe mineral oil and wet/dry paper.

Years of working as a programmer have left me with little in the way of endurance in my ligatures. Anything involving "elbow grease" is not a great idea for me. Even an orbital sander has too much vibration/takes too much down pressure for me.