On 1.8t originally fitted with ko3/s you also need to bend the pipe that runs alongside the block and feeds to the hoses for the heater matrix.
The ko4-023 has an egt bung on the housing and needs to be blocked up because our 1.8t golfs don't have egt sensor for the turbo.
You should also try and get ahold of the oil and water feed/returns from a 225tt, s3 or lcr, took me some time to source my parts for the ko4 upgrade on my AUM, got quite the bargain and thats the only reason Im going for the upgrade... honest

Managed to source a rebuilt ko4-023 fitted with ko4-022 housing with no egt bung, manifold, oil and water feeds/returns, 3" maf, s3 injectors for about £400 just made an offer for the dp and 3" intake pipe and waiting for an answer now. After that it's just an LCR fuel pump I need to source for my build.
After that no more power mods for me... except for the ecs lightweight pulley kit...
Also nathan.golf s3 injectors will fit into aum straight on, the s3 fuel pump will need modding to work properly in golf and no generally a 4 bar fpr is not needed for this! But a more precise answer is: it depends on your tuner.