Nice C1, the dynamic jaw looks significantly more stout than the earlier C1's. I don't see any pins holding the pipe jaws, are they removable?
The earliest C-series had two pins holding the pipe jaws. The next version had one set of pins. The most recent versions use spring clips on the back of the pipe jaws that fit into recesses in the jaw towers. You can pull them out with a big set of pliers pretty easily, and just push back in to replace.
The Wilton machinist and Combination vises were given a significant increase in size and strength when they updated the designs. I haven't seen an exact year that happened, but from all the Wiltons I've had, I would say it was in the mid-1970s. Early 1970s vises have the old shape/style and by 1976/77 they seem to be the more current style.
The earlier models have the more rounded dynamic jaw, which has a fairly large empty cavity. With the redesign the dynamic jaw is flatter, or more square profile, and has a very small cavity that's pretty insignificant. Part of that redesign also increased the area that surrounds the spindle collar significantly. It also recessed the collar into the dynamic jaw a bit, making it less likely to get hit and damaged.
There was another redesign around 1998 that eliminated the tail cap assembly that was a male plug fitting into the body of the vise that the nut went through. Now there is a round structure that fits completely inside the vise body, and the nut goes through that. A larger dust cap covers the entire assembly.
In short, the newest machinist vises are the strongest, and heaviest for a given model they have ever been. They are also much more consistent when it comes to things like casting accuracy, bolt hole spacing, etc, etc. I love the way the older Wiltons look, but they aren't as well made as the newest vises....contrary to what some folks might claim. I've seen older vises with keyways that were vastly oversized, not due to wear, holes for the jaw bolts offset .020 opposite from one another so replacement jaws wouldn't match up even remotely closely, main bodies cast offset so the swivel lock was nearly touching on one side, and well clear on the other, and the list goes on.
Guess I better put on my flame suit...lol.