Shouldn't have to mess with the bottom end. However you might need to reduce the compression ratio, either by messing with the head or fitting a a REALLY thick head gasket to reduce the compression ratio. Have a look on Minispares or Minisport or one of those UK parts websites. They sell a supercharger kit with a compression reduction plate. I think it's just a thick plate to reduce the compression ratio. I think the ideal is around 8.5 but it will all vary depending upon how much you've got the supercharger wound up.
Do a bit of a search on this forum and you'll see that the cost varies dramatically depending on what you want to do yourself. You can approach Link Automotive (
www.linkautomotive.com.au) and they do a lovely kit, but it is over $6,000.
The other option is you source a 2nd hand Toyota super charger and buy one of the kits that one of the guys on this forum was selling. Would cost a whole heap less but you would have to do a large part of it yourself, including find a suitable SC12 supercharger.
Another option is to look at Vmax Scart in the UK (
www.vmaxscart.co.uk). They do Bini supercharger kits. They modifiy a Bini supercharger and modify the head to reduce the compression ratio. They also put unleaded valves in the head at this stage. You'd need to check his website for details and freight might well be a killer.
There are many ways to skin a cat. It just depends on what you can afford and how much HP you really want, and what you want to get out of it.
There's heaps of info on this site if you look and on some of the uk forums as well.
Good luck and let us know what you end up doing.