POSSIBLE NMAC.

Narrative

BEING VECTORED FOR THE ILS RWY 19R SNA; HDG 090 DEGS; WE WERE ADVISED OF TFC. PNF (R SEAT) RESPONDED 'WE'LL BE LOOKING.' HOWEVER; WE WERE IMC -- SOLID. SECONDS LATER PNF POINTED TO THE L SAYING; 'LOOK AT THAT AIRPLANE!' I GLANCED L-HAND SIDE AND SPOTTED A CESSNA 150 PASSING OFF OUR L-HAND SIDE FROM FRONT TO REAR; APPROX HDG 240 DEGS; 200 FT HORIZ. OUR ALT (EXACTLY 3000 FT) IN THE CLOUDS. WE RPTED THIS EVENT TO ATC. JUST A FEW SECONDS LATER; PNF CALLED 'LOC ALIVE.' AT ABOUT THIS TIME AS WE WERE INTERCEPTING THE LOC I TOLD THE APCH CTLR I WOULD LIKE TO FILE A NEAR MISS RPT. WE WERE GIVEN A PHONE NUMBER FOR THE SUPVR ON DUTY AT SOCAL APCH AND I SPOKE WITH HIM APPROX 45 MINS LATER. I WAS TOLD THEY HAD FOLLOWED THE OTHER ACFT TO LGB; SPOKE WITH THE PLT WHO SAID SHE; A 30 YR FAA PLT EXAMINER; HAD US IN SIGHT AND THERE WAS NO PROB! THE SUPVR SAID THEY HAD LOST RADAR CONTACT WITH THIS AIRPLANE MOMENTARILY; SO MAYBE THEY FOLLOWED THE WRONG AIRPLANE TO LGB. QUESTION IF IT WAS THE WRONG AIRPLANE; WHY DID SHE SAY SHE SAW US? SUPPLEMENTAL INFO FROM ACN 304248: SOCAL APCH CALLED ME AFTER LNDG. MR. X AT SOCAL SAID A CITATION ON AN APCH TO SNA COMPLAINED ABOUT A NEAR MISS WITH MY ACFT. I SAW THE CITATION FROM THE TIME HE BROKE OUT UNTIL HE INTERCEPTED THE ILS FOR SNA N OF SNAKE AND OUTSIDE THE CLASS C AIRSPACE. NO EVASIVE ACTION WAS NEEDED. I ESTIMATED MY DISTANCE MORE THAN 2 MI FROM HIM. SOCAL GAVE ME AS TFC TO THE CITATION AS 11 O'CLOCK AND 2 MI. THIS CLASS E AIRSPACE N OF SNA IS CONGESTED.