I can tell you that a 270bhp engine will cost you at least £10k.
Then you need to spend almost at the same amount on the transmission, brakes, suspension, chassis etc etc.
Believe me - I know.
200bhp is more than enough in a Westie/locost etc, however if you got the time, cash and inclination then feck it - go for the 270! lmao
My engine will be about 235bhp (maybe 250)-plus 125bhp nitrous, then I'll transplant it into a Westifield/similar and change cams, followers and head gasket and go too 'higher'. How much higher is another question.....
Oh and i may or maynot drop the gas when it goes in the Westie as it could well be just unusable! lmao