Getsum

I have my scoobie's EJ20 engine torn down and found the no compression problem in a #4 piston edge blown. I can hone the very superficial cylinder scuff out but my only problem I have is not knowing which pistons go in my car. I know I have an EJ20 but the parts dealer said I need to know the serial number off the engine, and guess what, it's been filed off (not by me). I can only wonder why that was done . Short of pulling it apart and measuring the pistons, is there another way to tell which pistons I need? It is a 95 Jap import STI. Thanks Lee