Hi ramrod,
I did a few on Seiko sports 100's they are not too bad to do as the crystal stands proud of the bezel, so you can work them in the case (easier to hold), I have a 4 sided diamond sharpening block 200/300/400 and 600 grit depending on how bad the crystal is , but i usually start at 400 grit and grind out all the marks I can see, then on to 600 grit then I move to wet & dry paper on a sheet of glass and work through 800/1000/1200/1500 grit and finish with 2000 grit, then i polish with a felt buff on the dremel and Brasso.
Takes a bit of time and patience but they come up OK and as these are on vintage watches that are not going to be water proof thinning the glass is no real concern, a different matter with an active diver I would go with a new crystal, but for old Seiko's the new original crystal is worth more than the watch.
Max