My thoughts are that's a cast part. Although I'd say its cast iron (nodular like the vise most likely). I think a superior part could be made from regular hot or cold rolled 1018 or A36 steel, but there are a number of features that don't lend themselves to easy fabrication...the "sine wave" form, and the square hole. If you are really patient, files will get you there. If you are less patient, a die grinder and carbide burr is faster. If you are less patient than that, a machining center will do most of it except the square hole. Must broach or finish a rounded hole with files.
Personally, I'd try to bronze braze it with an oxyacetylene torch to get going for now.
