From what I was reading last night (as have a block I fancy splitting for a looksie), to remove the gudgeon, 1st remove the inspection covers, put pistons to Bottom DC, remove the circlip from the gudgeon pin and remove the pins. Do it in pairs. Once pins removed remove the pistons.
I also put up a post last night with workshop manuals,,,have a look at this :
http://www.ken-gilbert.com/wrx/STi_Manual/
Go to Engine - Mechanical - Section 20 'Engine Block'.
http://mysilvia.de/files/store/Artic...aru_Engine.pdf
Although the above is very lacking on the rebuild i.e it doesn't document reconnecting the pistons....LOL....