mrmiller:
Hopefully your didn't pay a lot for that project vise. Is that your first and only vise? Unless you are an accomplished welder accustomed to fixing cracks in cast iron, I would start searching for a better restoration candidate. Maybe you can luck out and find a replacement base for little $$. But if you need jaws as well as a base... (you know where I am going with this)
IIWY, I would look for a better vise to restore and keep the rusty Wilton under a bench somewhere until a new base and some jaws fall into your lap.
Another thing you could possibly do is to bolt it down to your bench without the swivel base. You can drill one more hole in the main vise body on the side opposite the swivel lock down bolt. You can fabricate your own soft home made jaws from aluminum or even hard rubber. Soft jaws are handy for clamping down smaller things that you don't want marred from jaw serrations.