They were designed for clamping things like sheet metal, looking at the condition in the photos, it's possible your father used them for clamping things like wood, was your father into wood work ?
Definatly modified by having the jaws (cleanly too) ground off. No clue on the use, likely specfic use.
They look like they have had their toothed jaws removed.
(to slow as always)
looks like they were used in some variety of sand/media blasting
Either he cleaned them up in a blast cabinet before his last use or these were used specifically when he blasted something.
The sides of the jaws are milled down. That was deffinatly modified by a machinist. Id say your dad may have just ended up with them. They were probably custom fitted for a specific task on a machine of some sort.
What does the center brace stamping say Mosstype? I think they were repurposed by a manufacture for original equipment distribution. Based on where you father worked and the products mosstype makes I'd say my hypothesis is valid.
http://www.mosstype.com/