No, not unless you want to get your rotary tool out and cut some metal. The Twelve Hundred won't even fit an EATX motherboard (12x13) let alone the S4985 (16-and-something by 13-and-something). The only cases I've seen people use with good luck are Cooler Master Stacker 810s and expensive server cases like that Chenbro unit GhislainG linked to. I know this as that board got me thinking about perhaps doing a quad-socket setup for my next machine. I'll build my own case if I do in fact go that route as I can make a nice wooden cabinet from some inch-thick pine and some metal parts from case mod sites (HDD cages, switches, 5.25" bay hardware) that will suit my needs a lot better than a super-expensive SWTX/SSI MEB rackmount server case like that Chenbro.
A few pieces of advice about that particular board:
1. It only takes Opteron 8200 series dual cores and the 65 nm quad cores (model numbers 8347-8360.) It does NOT take the newer 45 nm quad (8374-8393) or any six-core units (Opteron 8400 series.) If you get this board, go pick up some Opteron 8356s or 8358s from eBay for about $80-100 apiece and make yourself a nice unit for a pretty low price.
2. You need a PSU around 1000 watts with two 8-pin EPS12V connectors. If the PSU only has one EPS12V adapter, you need to get an 8-pin PCIe-to-EPS12V adapter.
3. Dynatron F558s are about the best "native" Socket F heatsinks that don't cost an arm and a leg. Noctua's UH12DOs are the nicest ones out there bar none, but they're about $70 each compared to a bit over $20 each for the Dynatrons.
4. You will want to get at least 8 sticks of registered ECC DDR2-667 RAM. Normal unbuffered, non-ECC desktop DDR2 won't work in this board.
5. You will need to run either some sort of Unix (Linux, BSD, Solaris) or Windows Server to see all of those CPUs. Windows XP, Vista, or 7 Home versions only allow one CPU socket; the Business and Ultimate versions allow two sockets. Windows Server is about $1000 per copy last time I checked and certain versions have certain RAM restrictions.
I'm setting up a server with the same motherboard & the 8356s mentioned above and after looking at the case options have decided to modify an existing rack-mount server case to handle the meb form factor.
They are :
cheap(if you can find one within driving distance),
come with a ready supply of industrial grade fans and power supplies,
and last but not least - these older cases were made to house computers that cost in the tens of thousands so as you might guess they are VERY well made.
I'm considering making a few extra myself and seeing how they fare on ebay. Shoot me a line if you're interested and you'll help make up my mind. specialkehoe at gmail.