Simples, measure one. People have stuck V6 engines in, Flat fours, Allsorts, there is certainly space for a Fireblade engine as its only the size of PC 
, but you will still need to fabricate mountings and work out how to make it actually drive the wheels, are you planning on chain drive?
I dont think you can run a chain drive if you mount a bike engine in the engine compartment. The engine needs to be mounted with the drive side facing forward so it can be connected to the drive system. I have a mid mounted 1300cc suzuki engine in my fiat, but i'm also in the planning stages of dropping a 1000cc gsxr engine in the back of one of my nikis as i would like a standard looking vehicle from the outside.
This is how i plan to do this mod: Parts being used - 1000cc GSXR Suzuki Engine, R200 Nissan S15 Silvia IRS Diff & driveshafts, Nissan S15 tailshaft, about 5mts chrome moly tube.
What i think i'm going to do: To mate engine and diff together i plan to use the tailshaft from the nissan, shorten it to the required length, and modify it to accept the splined shaft that the drive cog bolts to. The end that bolts to the diff will be a standard bolt on. Once that's done I'll dummy mount the whole assembly to see how it sits, fit the driveshafts to see how long they need to be & get them machined to fit the original splines on the fiat. Then its a matter of fabricating mounts for engine and diff.
What comes next - gearchange, clutch & accelerator mechanisms. Gearchange will be up/down shortshift style and I utlised the original shifter and shifter position on my mid engined car and it works very well. I still havent figured out how i will convert the backwards/forwards motion of the gearstick to an up/down movement as the engine is mounted sideways (some sort of rocker system i'm thinking). Clutch is hydraulic and i will simply get a longer hydraulic line fabricated and mated to my clutch pedal with the original clutch lever mechanism from the bike (have this setup in my other car and it works really, really well). Accelerator is cable and just needs an extension from engine to pedal.
Then there's other things like a reverse gear etc....
As for fit, I'm sure you shouldnt have any issues with a 600cc engine as an R1 yamaha engine fits in sideways, with just the bootlid opened a tad. I plan to cut my bootlid and fit the wind catcher scoops you can get for these if i have clearance issues.
You shouldn't need to cut anything out in the engine compartment, the gearchange mechanism may need some mods to the body though.
Hope that helps
Cheers
Dan.
