Wow. Cool box.
For your proposed 23" screens... have you looked at the Apple Cinema Display? That's what I'm using, it's great quality 1920x1200 and cheap! Only caveat is that the Parhelia doesn't work with it in low-res modes (i.e. boot screen

) but I have a 15" trinitron for that.
I see very many blocks on the market which state Opteron or "socket 940" compatibility... for example at
http://www.xice.de/ or chillblast I mentioned above. It's not so much a problem of individual components, as not knowing where to start and what I need in total.
At a guess:
2 processor blocks
some tube
GPU block ( noise reduction! )
12V pump
reservoir
some screws. ... ???? what kind?
but there are so many options, and no easy kit with all that in it. I have zero experience and am doing this for practical reasons.. not for fun, so I'd like it as easy as possible!
The xice kit looks almost perfect... except the cooling unit is on the outside of the case. I don't like that idea.