That looks to me like something from the Meadville vise co. That company turned into Yost sometime around 1910 if I’m not mistaken.
So your gramps vise dates to the turn of the century and is a wonderful survivor that deserves preservation. Please don’t bead blast it and paint it bright red. Gentle cleaning with dilute simple green or similiar product, then dry thoroughly and rub on some boiled linseed oil to retard rust and give it a well cared for appearance.
That chunk of wood probably acted as a spacer to compensate for a less than super thick work bench or table.
You’re luck to still have the big wing nut. Those are often lost.
The metal disc is to assist with the lock down when that big wing nut is tightened to prevent unwanted swiveling while the vise is in use. They are called Swivel Base Plate. Factory? I doubt it. Original ones have holes to screw down to the bench. Yours has a big slot. But I defer final judgement until others more knowledgeable than I have a chance to respond to your questions.
I have a couple of vises like that with the through the bench mount. They have a grooved metal plate that goes between the vise body and the bench top.
If I were you, I wouldn’t use that vise for any heavy duty work but give it a place of honor and possibly an opportunity to perform easy tasks befitting its age.
You have one or two other vises to do the “heavy lifting” right?
.---But just the vise.
