Engine transplant options for Spitfire?

[spartacus]

A mate of mine has a Triumph Spitfire, MkIV I think, and he is looking for any ideas on what engine he could replace the Triumph 1500 with that without having to modify the chassis or bulkhead that would produce significantly more BHP than the original lump and was lighter? obviously engine and gearbox mount changes would be expected.

Alternatively does anyone have any ideas about supercharging?