Drawing a Mounting Flange

In order to used my grandfather's giant old Prentiss vice that weighs what seems like at least 100 pounds, with a jaw that opens up at least a foot maximum, I have to figure out how to mount it onto a work bench that I as yet do not have.

I am hoping something basically three foot by six foot constructed with 4 x 6 inch timbers will do the trick. I may yet have to put an anvil on the other side or something. Most places I have seen something approaching this size were overlaid with metal so that welding could also be done on it. I imagine some cementitious tile underlayment could also insulate it. For now I plan on laying one by six pine diagonally across it with 1/2" marine grade plywood on top framed by two by fours it will still require four bolts five inches long to secure this monster, which I can only imagine was used to work on steel railroad pieces or girders.

The last export photo was what I thought I could send to a machinist that would swing a little past square to the table each way. It will be simpler to just drill three holes for three positions.