ACR-LGT AND CPR-LTT BOTH TAKE EVASIVE ACTION TO AVOID COLLISION.

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LTT X WAS AT FL330 INBND TO JNU FROM THE W. LGT Y WAS AT JNU REQUESTED DEP VIA BARLO 4 YAK J501 ANC FL350. HE SAID HE WOULD ACCEPT A VFR CLB TO ANY ALT. I CLRED LGT Y TO BERGS DME FIX; NO DELAY EXPECTED; CLB TO 17000'. I CLRED LTT X TO FL190. AFTER DEP I RECLRED LGT Y TO 12000' AND TOLD HIM TO EXPECT HIS REQUIRED ALT WITH A VFR CLB THROUGH 17000' WHEN I HAD LTT X OUT OF 16000'. I CLRED LTT X TO 13000'. WHEN LGT Y RPTED LEAVING 14500'; I CLRED LGT Y TO ANC VIA FLT PLAN TO MAINTAIN VFR THROUGH 16000'; THEN CLB TO FL350. I CLRED LTT X FOR APCH. I THEN RECLRED LGT Y TO MAINTAIN VFR THROUGH 16000'; THEN CLB TO FL310 BECAUSE OF TFC OVER YAK AT FL350. I THEN SAW LGT Y; LIMITED DATA BLOCK; ABOUT TO MERGE WITH LTT X; BUT DIDN'T HAVE TIME TO ISSUE TFC BEFORE THEY MERGED. LGT Y WAS ABOUT TO REQUEST LTT X'S POS; BUT HAD TO BREAK OFF HIS XMISSION TO TAKE EVASIVE ACTION. LTT X THEN RPTED HE HAD TAKEN EVASIVE ACTION TO AVOID LGT Y. LGT Y WAS NOT YET RADAR IDENTED. I WAS ABOUT TO ISSUE A NON RADAR TFC ADVISORY WHEN THE ABOVE EVENTS OCCURRED. LTT X HAD JUST BEEN SWITCHED TO TWR; BUT HIS RADAR SVC NOT YET TERMINATED. HIS TARGET WAS COASTING OFF AND ON SINCE LEAVING 16000'. HAD I KNOWN THE ACFT WERE ALREADY SO CLOSE I WOULD HAVE WAITED FOR DME PASSAGE INSTEAD OF A VFR CLB. I SHOULD HAVE ISSUED A TFC ADVISORY TO BOTH ACFT; PERHAPS BEFORE ISSUING A VFR CLB. HOWEVER; BOTH ACFT WERE AWARE OF EACH OTHER; AND SINCE LGT Y ACCEPTED A VFR CLB; I WAS LEGALLY AUTH TO DISCONTINUE IFR VERT SEP. LTT X SAID BOTH ACFT WERE ON THE LOC AT 13000'; HEAD ON AND BOTH MADE EVASIVE LEFT TURNS. LGT Y APOLOGIZED TO LTT X AND TOLD ME HE WOULD HAVE APPRECIATED A TFC ADVISORY. I CONCURRED. MY RECOMMENDATION IS THAT WHEN USING VFR TO SEPARATE ACFT; THAT TFC ADVISORY BE ISSUED PRIOR TO ISSUING VFR CLB OR DSCNT TO SEE IF ACFT WILL STILL ACCEPT THE VFR ASSIGNMENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR CTLR WAS SURPRISED BY HOW CLOSE THE CLBING ACR LGT GOT TO THE DSNDING CPR LTT BEFORE VERT SEP WAS NO LONGER A PROB. IN THIS AREA OF THE CENTER'S AIRSPACE; RADAR COVERAGE IS SO POOR; BECAUSE OF TERRAIN NEAR THE RADAR SITE; THAT CLBING ACFT CANNOT BE IDENTED UNTIL THEY LEAVE 15000'. THE INBND LTT HAD ENTERED THIS AREA AND RADAR SVC HAD BEEN TERMINATED BECAUSE THE CTLR WAS LOSING COVERAGE. A VFR CLB WAS GIVEN TO THE ACR BECAUSE THE CTLR THOUGHT THE 2 ACFT WERE STILL VERY FAR APART AND WOULD NEVER BE A FACTOR FOR EACH OTHER. THE FAC PROCESSED THIS AS A NMAC AND NOT AN OPERROR. RPTR CTLR'S EXPERIENCE LEVEL WAS ASCERTAINED DURING THE CALLBACK.