Re: Not for my money.
If you want scary - you can get an off the shelf kit that can pop a Suzuki Hayabusa motorbike engine into a classic Mini with no body modification. http://www.vetech.co.uk/hayabusa/
From that website :
190bhp (normally aspirated) through to a potential 360bhp (forced induction) at the wheels
6 speed, semi-automatic sequential box including reverse
Limited slip differential
Base engine weight less than 100kg