NMAC BTWN A WDB ACR ACFT AND AN SMT TWIN ENG ACFT NEAR A BUSY TERMINAL AREA.

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I WAS THE CAPT ON A SCHEDULED CARGO FLT FROM ATL-SDF ON DEC/TUE/93. OUR POS WAS THE IIU 131 DEG RADIAL 28 MI; HDG 311 DEGS; ENRTE TO SDF. WE WERE IN CONTACT WITH STANDIFORD APCH CTL AND WERE GIVEN A CLRNC TO 7000 FT. PASSING 7700 FT; APCH CALLED AND SAID 'MAINTAIN 8000 FT TFC 12 O'CLOCK 7300 FT.' THE FO STARTED TO MAKE A CORRECTION BACK TO 8000 FT WHEN THE FE SPOTTED OUR TFC AT 12 O'CLOCK ABOUT 200 FT BELOW AND 200 FT HORIZ SEPARATION. WE MADE AN ABRUPT NOSE UP INPUT. I ASKED THE CTLR WHY HE HADN'T GIVEN AN EARLIER WARNING AND I WAS TOLD THE TFC JUST SHOWED UP ON THE SCREEN. THE OTHER ACFT WAS A LIGHT TWIN; RETRACTABLE GEAR; BLUE AND WHITE; HDG ENE. I BELIEVE HE WAS AT 7500 FT FOR THAT DIRECTION OF FLT. LESSONS: THE IMPORTANCE OF CLRING AND LOOKING FOR TFC. WHEN GIVEN INSTRUCTIONS TO RETURN TO AN AMENDED ALT; DO SO AGGRESSIVELY. DON'T ASSUME THERE WILL BE TIME TO AVOID THE TFC CONFLICT. THE ABSOLUTE NEED TO INSTALL TCASII ON ALL CARGO ACFT IN THE UNITED STATES. THIS NEAR MISS WOULDN'T HAVE OCCURRED IF WE HAD TCASII.