This is what Godspeed said -
"Yes we have sold the fitting kits to owners of the B4s , and no one has come back to me saying they didnt fit so I assume everything is ok , if your car has the 266mm discs , then the 290mm WRX discs and 2 pots should fit fine"
So if standard B4 rear discs are 266mm are all classic shape Impreza 2 pot rear discs 290mm?