Rock Island 74a vise information?

[mcoz]

I recently acquired a nice little Rock Island no 74a vise. I began taking it apart, but paused to look into it a little bit. Trouble is, information on this model is scant at best. I know the vise has 4.5" jaws, permanent jaw inserts, swivel base, and weighs around 65-70lbs. The vise has "20" stamped in both the dynamic and static jaw. In addition, the end of the slide has "94" cast in it. Finally, the bottom of the swivel base has 74c cast in it. There is no evidence of a Birtman Electric tag.

Any information on this vise anybody?