AMERICAN FLT 1180 (MCDONNELL-DOUGLAS DC-10) WAS NORTHBOUND OVR THE ATLANTIC OCEAN AT FLT LVL 350 AS A BRITISH ROYAL AIR FORCE VICKERS VC10 WAS CRUISING EAST AT THE SAME ALT (NON-STANDARD ALT FOR THE VC10'S DRCTN OF FLT). THEY WERE IN A NON-RADAR AIRSPACE UNDER CTL OF NEW YORK ARTCC, USING NON-DIRECT RADIO COMM THRU ARINC. BOTH WERE IN VMC, ALTHOUGH OPERG UNDER IFR RULES. THE 2 ACFT CONVERGED AS THEY CROSSED OVR ELWOD INTXN. THE VC10 PASSED IN FRONT OF FLT 1180, FM LEFT TO RGT, WITH LESS THAN REQUIRED IFR SEPN. NEITHER FLT CREW SAW THE OTR ACFT UNTIL FLT 1180 FLEW THRU THE WAKE FM THE VC10. THE CREW OF FLT 1180 THEN SAW THE VC10 FLYING AWAY AT THE SAME ALT WHICH THEY ESTD WAS LESS THAN 1 MI AWAY. THE STRIP FOR THE VC10 WAS MARKED WITH A RED UNDERLINE & AN ARROW TO DEPICT ITS DRCTN OF FLT & NON-STANDARD ALT. THE CTLR SAID SHEWAS AWARE OF THE VC10, BUT DIDN'T SEE THE STRIP FOR FLT 1180 IN THE BAY FOR ELWOD INTXN. WHEN THE CTLR ASSUMED HER DUTY PSN, THE PREVIOUS CTLR TOLD HER THE VC10 WAS CLEAR (HAD NO CONFLICTING TRAFFIC) THRU STOCK, ELWOD & DEENO INTXNS.