NMAC BTWN A BEECH 33A ON FINAL; FROM A L BASE LEG; AND A BOEING 75 STEARMAN BIPLANE; TURNING FINAL FROM A R BASE LEG. ANOTHER PLT WARNED THE BEECH ON FINAL THAT ANOTHER ACFT WAS ABOUT TO CRASH ON TOP OF HIM. WHEREUPON THE BEECH OBSERVED THE STEARMAN IN HIS WINDSHIELD AND THEN DSNDED AND TURNED THE ACFT TO THE R.

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AT DUJ ARPT MANY AIRPLANES WERE IN THE AREA AND IN THE PATTERN WHEN I FIRST ANNOUNCED MY POS AT 6 MI N OF THE FIELD AT 4500 FT MSL. I HAD PICKED UP THE AWOS AND LEARNED THEY WERE USING RWY 25. I PLANNED TO OVERFLY AND DO A L DOWNWIND TO LAND. I ANNOUNCED WHEN I WAS OVER THE DEP END OF RWY 25 WHEN ANOTHER ACFT; SMA Y; STATED HE DID NOT HAVE ME VISUALLY AND WOULD DO A 360 DEG TURN. I ANNOUNCED MY POS ON DOWNWIND; BASE LEG AND A 3/4 MI FINAL. I WAS AWARE OF AN ADDITIONAL ACFT ON THE LOC FOR RWY 25 WHO WAS BEHIND ME. THE FIRST KNOWLEDGE I HAD OF AN IMPOSING PROB WAS WHEN SMA Y PLT CALLED ON CTAF (123.0) STATING; 'ACFT ON FINAL AT DUBOIS; 1 ACFT IS ABOUT TO CRASH ON TOP OF THE OTHER!' KNOWING I WAS ONE OF THE ACFT (BEECH BONANZA F33A); I QUICKLY LOOKED TO THE FRONT; SIDES; UP; DOWN AND SAW NOTHING. WITHIN ABOUT 4 SECONDS OF THE RADIO MESSAGE; I HAD A WINDSHIELD FULL OF AIRPLANE (A STEARMAN). THIS AIRPLANE CAME FROM ABOVE AND MY R AND BRIEFLY LEVELED ABOUT 20 FT IN FRONT OF ME. MY POS AT THIS TIME WAS APPROX 200 FT AGL AND 500 FT FROM THE APCH END OF RWY 25. FOR ABOUT 2 SECONDS I DID NOTHING; AND MY FEAR WAS I WOULD BE TOO FAST AND RUN INTO HIM. WHEN THE COLLISION DID NOT OCCUR; I QUICKLY TOOK EVASIVE ACTION WITH A DIVE TO THE R; FOLLOWED BY A CLB WHICH TOOK ME OVER THE TERMINAL BUILDING AND THEN CLBED TO PATTERN ALT FOR A L DOWNWIND TO A FULL STOP LNDG. THE OTHER ACFT JUST AFTER THE NEAR COLLISION DEVIATED L AND CAME AROUND FOR A FULL STOP LNDG. IMMEDIATELY FOLLOWING THE INCIDENT I HAD A BRIEF CONVERSATION WITH STEARMAN PLT. MY UNDERSTANDING IN TALKING WITH HIM IS HE WAS DOING A R DOWNWIND ENTRY AND WAS NOT AWARE OF MY POS. WE ARE GOING TO MEET TO DISCUSS THIS INCIDENT IN DETAIL SO THAT WE BOTH MAY BECOME BETTER PLTS FROM IT. SUPPLEMENTAL INFO FROM ACN 402453: AFTER DISCUSSING THE INCIDENT; WE BOTH HAD RPTED POS OVER THE RADIO.