You may have more luck finding details of mods if you have a look on a Mazda or some of the Jap forums, the SP20 is basically the same car with just cosmetic differences
By the way if you go with extractors you may need to make some minor modifications to make them fit and you could also expect some error codes to show up. I had a set of Genie headers fitted to an SR2 I owned and to be honest I didn't really notice a great deal of difference to performance but I think it made it even thirstier on fuel than when stock. I had other issues with mine due to an obvious lack of maintenance on the behalf of the previous owner although the log books were up to date and stamped I suspect the books may have been fixed :( I traded the car about 3 months later and haven't seen it anywhere since
