With the limited info in that advert, all we can do is to make some 'educated guesses', based on that photo.
Early 1900's?.....no, could be late 1930's to mid-'50's, most likely 1940's, part of the high-volume production of tooling during the war.
HP and wheel size?......it could be a 2 or 3hp. 1750rpm unit, for 12" wheels, or a 5hp 1150rpm unit, for 14" wheels. I'd guess, based on the size of the data plate relative to the motor, that its not the common smaller 1hp 1750rpm unit, for 10" wheels.....but could be mistaken.
The seller's 'bad capacitor' diagnosis? A 3-phase motor, which this one most likely would be, will 'hum' and not turn if two of its three wires are 'hot' but one has no voltage. A 3ph motor tried on residential single phase 220 will do that, of course.
It could be possible that what appears to be another motor in the background was an earlier owner's rig for an improvised 'rotary phase converter', in which an 'idler motor' would be spun, then energised, to provide the 'third leg' of the power, which does start and run a 3ph motor, such as that grinder. This improvisation, if that is what is present, would be a practical way to run a 3-phase industrial grinder on domestic 'single-phase' 220 power.
Its also quite possible that the photo simply caught an unrelated motor in the background.
Another caveat would be that many of that style of grinder were built as 'single voltage' units, wired for 440V only, and must be re-wound to operate on 220. If otherwise in good condition, they are well worth the cost of re-winding.
The Hisey-Wolf make is best quality equipment, so, if this one has no cracked castings or other damage, it is would be well worth the cost of re-winding, new bearings, and new wheels, if one has a need for a grinder of this size class. (for a cost-analysis, look at the price of a new 12" Baldor pedestal grinder)
That said, its present economic value is that of its weight in scrap, as the cost of rebuilding will equal or exceed its potential market value, that is, it would be cost-effective to rebuild for one's use, but not to sell.
cheers
Carla
