You should have a letter on the chassic code right after the GC8
as g = model impreza
c = body type e.g saloon coupe.
8 = engine 2.0 turbo (6 = 1.8,4 = 1,6)
the letter which you havent put = year (A = MY93, B = MY94, C = MY95/96, D = MY97, E = MY98, F = MY99, and G = MY00)
the next number denotes the doors the car has. 2 = two door coupe, 4 = four door sallon, and 5 is 5door sports wagon.
after the its model type. 8 = WRX, 7 = RA, E = STI (From version III), D = STi type R and RA and S = 22B
The last didget is either a D for 5speed manual or P for four speed auto.
All of this is based on a calassic.
And the 7 diget chassis code for my P1 should be GC8G2DD
Hope this Helps Regards Monki.