A truck engine in a car?
I know it sounds a bit ridiculous but as a what if...
... you would build a car around a truck engine. By truck I do not mean some mid weight pick-up but a propper lorry. Say the D16E engine from the Volvo FH16-660.
The advantages? Well at 3100NM torque it will be hard to beat. And it gets 660hp out of the box. And it is emission compliant, totally unstressed and made to last forever. And as related to engines they put in coaches, it can be mounted lying flat - so could be mounted in an underfloor configuration.
The downsides? Well it weights around 1400kg, so that is definitely one. Getting 3100NM to the road might be another 
Making a chassis strong enough to hold it, yet light enough for the overall vehicle weight not to exceed 3 tonnes might be a challenge.
As an aside, has anyone ever fitted a truck engine to a car? The two similar examples I could find were a RR Meteor powered one (cannot remember the name) and the Tank car, with an M47s engine (IIRC).