BE35 AND PA34 HAD LTSS WHEN TWR LCL CTLR HAD BOTH ACFT ON FINAL FOR THE SAME RWY.

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L BASE FOR RWY 34; #2 WITH KING AIR #1; RPT L DOWNWIND TO L BASE. (KING AIR WAS ACTUALLY R DOWNWIND AND BASE.) TWR ADVISED 'IFR TFC WAITING TKOF ON RWY 34; CHANGE TO L DOWNWIND FOR RWY 30.' FLEW L DOWNWIND AND BASE TO RWY 30. IN POS TO TURN FINAL ALMOST; WHEN SAW TWIN 1 1/4 - 2 MI ON 280 DEG COURSE; APPARENTLY FOR RWY 30 LNDG. WE BOTH TOOK EVASIVE ACTION. TWR ADVISED TWIN CONTINUE TO LAND; WITH ME #2. MADE 180 DEG AND 360 DEG FOR SPACING AND LANDED. SEVERAL CONTRIBUTING CAUSES TO EVENT: TOLD EXPECT RWY 34. TWR CALLED KING AIR TFC INCORRECTLY FOR RWY 34; CHANGED MY ASSIGNMENT TO RWY 30 WHILE I WAS ON VERY SHORT BASE TO RWY 34. HEARD SUBJECT TWIN CALL 1 1/2 MI E OF NAVY GLENVIEW; BUT HEARD NO 'CLRNC TO LAND RWY 30' AND WAS NOT EXPECTING CONFLICTING TFC. TWIN HAD SUN IN EYES AND WAS VERY ALERT TO SEE CONFLICTING TFC -- ME. TWIN WAS NOT ON STRAIGHT-IN PATH FOR RWY 30. 2 TIMES I WAS ON SHORT BASE -- PERHAPS COMMITTED TO LNDG MENTALLY; AND LOST TFC AWARENESS. THIS IS VERY BUSY ARPT WHERE OFTEN TIMES TWR DOES NOT CLR YOU TO LAND UNTIL ON SHORT FINAL. NOT A GOOD PRACTICE FOR ME (PLT) OR TWR CTLR. PERHAPS DEPEND TOO MUCH ON TWR FOR SPACING AWARENESS AND NOT ENOUGH ON MY (PLT) SPACE AWARENESS.