what do you mean by slim? If you don't have low profile cards, than maybe you can use a 2u Server chassis with a riser card. But you would need standard type isa PCI riser with paddle boards. that could be difficult or impossible to find. I'm just assuming its a standard AT board, if not than you are need to do serious customization and thats not something that can just be suggested by off the shelf parts and youre on your own there.

I cant find any pics on the 600 but does yours look something like this?

If so then it's the LPX form factor so about as slim as you can get. It's also not an official form factor much like SFF today so any case you do get will have to be customised.
On the plus side I'm assuming cards plug into a raiser card? That drops your required height to whatever the raiser card is.
Then it'll be the motherboards that dictates the other dimensions.

chinny22: that's the one mate!

yeh so motherboard will dictate width and depth, raiser card will decide your height.

I actually really like the LPX dimensions, already pretty portable compared to tower cases and fits just right under my arm. They stack really nice as well if you happen to own 3 😉
But if still want to go smaller then yeh, your going to have to do a fair bit of hacking of an existing case or start from scratch.

Thanks guys. I'll do some measurements and report back, still looking to move the guts into a newer Lenovo ThinkCentre, add a MHz display and some nice 3D logos on the front.