Or, cost a ridiculous amount to pull off (like a Z-06 engine in a VW beetle should cost millions.)
The Hollywood actor Paul Newman done this back in the 60's or 70's - and it didn't cost millions.
He had a early 60's convertable bug he bought from new and got a race team to stick a V8 where the rear seat and luggage space would normally be.
It was recently sold on a famous Aircooled V-Dub website called Oldbug.com - big up Randy
There's many crazy Aircooled dubs flying round with everything from V8's, V6's cossie 4 pots and even Turbo Impreza engines and a porsche 996 drivetrain (albiet this last one was a project - not sure if it ever got finished).
It won't cost millions, VW Beetles have such simple desgign + the body is bolted to the chassis, it'd be very easy for people who have the right experience, qualifications and tools for the job, and certianly wouldn't cost anywhere near a million ££'s or $$'s.
you can probably fit the w16 in the back

i wish my g27 was compatible with an xbox i loved putting a 800bhp motor in my late 70's camaro. i will never play forza gain cause i dont have the cash to get a 360 wheel and controller play is boring
There's a W12 Lupo flying around.. Loads of 1.8T'd Lupo's aswell pushing 300bhp or more.
In general - as mentioned on the two engine swap threads already, feasible and popular engine and drivetrain swaps that are regularly carried out in real life should be looked into by Polyphony.
But then again when the tuning is as ridiculous as it is on GT5, I think we're banging our heads against the wall, they can't even get tuning right for normal cars, so don't get your hopes up for engine swaps.
How come there's a HPA twin turbo Audi TT & Golf, but you can't charge the MKIV R32 - yet how many hundreds or thousands of R32's have been 'charged in real life throughout the world??
ECU chip on a Schwimmwagon, Samba and Split - nice........ yes, of course.. Oh look, ABS and ASM etc etc too... WOW, I'm sure when Ferdinand Porsche put the lil ol bug together he hid these things somewhere where millions of owners would never find them for the next 70 years and more.
Yawn...sigh...roll eyes.....
I'd absolutely love feasable and realistic engine / drivetrain swaps to be in the game - I just can't see Polyphony doing anything other than their own agenda.