is there a greddy header for the 03 gt
according to the official greddy website which you can view here:
http://www.greddy.com/products/products.asp?makeidx=4&model=64 there are only these products available by greddy for the '00-'04 toyota celica gt:
Product Type: Evo. - Exhaust Systems
Model: Celica GT 2000 - 2004 EVO Cat-back
Product Type: SP2 - Street Perfomance Ver. 2 (NEW)
Model: Celica GT 2000 - 2004 SP2 Exhaust
Product Type: Evo2 - Evolution Exhasut System Ver.2 (NEW)
Model: Celica GT 2000 - 2004 EVO2 Exhaust