That is exactly the problem.
I have now hoisted the beast out of the boot of the Jag (if my wife finds out how I brought it home, she will not be happy) and set it on a work bench for cleaning. With a little wire wool and WD40 it's looking half decent now.
The base isn't actually solid. I think it's cast iron and it has a sort-of web-like pattern, so cutting might not be as much of a nightmare as I'd first supposed. I am, however, still reluctant to chop it up because I don't need to ( I have a decent machine vice already) and it seems a shame to destroy it.
The three vices have, I think, been used to hold a part with a specific shape. The rear, fixed, jaws all look to be original and are aligned. Each of the three moveable jaws has been modified. I guess that the vice bank was set up for making something that had a particular shape and, when the job was done, the company simply got rid it. Either that, or there were three milling processes, each requiring differently shaped jaws.
I think that one could buy, or make, more conventional square jaws without much difficulty, so that all three of the vices still have useful potential. I imagine that, if one wanted to work on a long part, the set-up could give superb rigidity.
If anyone is interested in the detail of the jaws, I'll go out to the workshop and take some more pictures.
It's a devil of a heavy lump. At one point I had it on a sack truck, with a chain around it to stop it from falling forwards. I laid the sack truck down and it nipped the chain against the truck: I couldn't even lift the end by an inch to get the chain free.... If nothing else, I've bought a cheap anvil!
Kind wishes,
Nick