It's aftermarket most likely. He told me it was a TRD piston and it looks a lot like the piston in this thread
http://www.aeu86.org/viewtopic/stran...s-4a-ge/t/6212.
The weird part is it was just about as fast as my girlfriend's 1986 AW11 i'm driving currently. Then again I never really gave it hell at the top end.