The newer big blue vise looks like a model 500. It's an easy cheat, 5" jaws = Model 500... usually.
It's a 60176 vise so probably in the 70's like the other one.
The dynamic jaw screw should come out rather easily, unless there is gunk on it:
-remove the three retainer plate screws (behind the "handle") and the lead screw should come all the way out. If it doesn't it may be full of gunkyness (word?) or have some damaged threads.
-the jaw should slide right out once the lead screw is out. If it doesn't, it may have more gunk on it.
(**Liberal use of penetrating oil works wonders on these things... . for a great but rather politically incorrect homebrew penetrant, a 50/50 mix of ATF and acetone works awesome)
-once the jaw is out, you can remove the end cap. or nose cone, or dust cap. whatever you wanna call it. whack it out/off with a wooden dowel, hammer handle, etc.
-now you can find either the cross pin, cross pins, or machine screws that are holding the "nut" into the vise. The "nut" is the threaded tube that the lead screw threads into. If your vise has machine screws, the heads are usually obvious, unless they are broken off, then maybe not so much. . The cross pin(s) can be tapped out with a punch, the machine screws sometimes need to be drilled.
(**I can see the little hole in George's first picture that looks like a cross pin hole. )
-once those are out, then take another slightly larger dowel or hammer handle and smack the "nut" out of the vise. You'll notice a groove in the "nut" that aligns with the cross pin(s)/machine screws.
Now the vise SHOULD BE completely disassembled in a big pile of gunky rusty old stuff awaiting tender loving care, new paint, and fresh super slippery lubricant. We'll save the brand and type for another grease/lube war thread later. :-laf
Hope this helps and works... if not, use gunpowder. just kiddin'
Dan-