N/A really depends on how hardcore you want to go - it is not necessarily the cheapest/most cost-effective option (bar insurance issues) - the usual breathing mods will get you to ~100bhp, getting over that hasn't really been done on the road (bar the NME Micra) as to go higher you will need cams, these will need management to run to their best, if you go for cams, you might then as well put a larger throttlebody on - or even individual throttle bodies - this has (AFAIK) *never* been done on a UK road car (bar Boggs Bros. carb conversions), which will require custom hardware and, again, a remap; once you've had this for a while, you'll want more, next step is pistons and headgasket, although high-comp. pistons are not available for the 1.3 (1l pistons will fit, but - again - has not been done in the UK and you may run into piston/valve clearance issues) so you decide to go for the CGa conversion, you'll need to source an engine, then get the pistons and rods and then find a thinner headgasket, you may even want to get hte head ported at this stage.
Now you have a spanking N/A engine, that will only run on premium fuel (not really a problem) but if you want to keep taking it to 8k every day, the crank is the weakest link - a custom crank will set you back an eye-watering amount of cash.
It all depends how much power you want to achieve and, maybe more importantly, what your budget is - as Anthony said, you can buy each N/A bit separately and slowly increase the HP of your engine on your car to spread the cost, however this is probably better achieved by driving a standard car and making a transplant engine in your garag to put into your car when you're finished (if you haven't lost interest/money by this point).
Probably what is best is if you could get aride in a decent N/A and turbo'd cars to see which form of power delivery you like best so that you don't end up slightly disappointed with your completed project.
Sorry for the essay, has been in my head a long time, Craig
