Thanks everyone!
I got my car certified last week and it's now 100% legal :D. You only have to get a cert done if you install coilovers or do an engine swap etc, so when I had mine done I got the engine, coilovers, brakes and a couple of other things put on the cert plate to avoid any trouble with the cops in the future.
I also scored a genuine TRD fuel cap yesterday. I've always wanted one but had other things to spend money on for the car instead, so when I managed to get my hands on this one for free I was pretty happy: