What gearbox do you have? What is it out of?
But yeah, as I said, it's probably going to be an issue for you with engine choice... and you may have to cut up the firewall and floor for the gearbox, tailshaft and such... then you'll need to mod the back end to suit an axle... You would probably have to take the fuel tank off to do this (Assuming the fuel tank is under the ass end, like my civ) In which you could probably custom make one to fit in the boot.
So all in all, you'd need to fab a lot of the body probably, source a rear axle (independent possibly... may need to source a leaf spring one. I don't know much about s600's) and diff, and hubs and stuff to run off that. Not sure if the front hubs could be closed over on the back, and just be left as is. Would also need to custom make brackets and stuff for the engine, and if it ends up being longer than the bay, fab that up a bit. find somewhere to mount the radiator, battery, etc etc...
Worst case scenario, it could end up being a massive pain in the ass, and be a lot of work. Best case scenario, it could cost you <5k (just a guess) and you could have an awesome little car.