3 dim lights in triangle shape, about 400 ft high, moved west to east slowly along S. shore of Fire Island, NY

My Father was a park ranger at Davis Park on Fire Island, South of Patchogue, Long Island, NY in the Summer of 1967.  A younger brother and myself (ages six and twelve respectively) stayed with him then in the months of July and August.   One night (I don't remember the exact date), my brother and I were in our sleeping bags talking and looking up at the sky before falling to sleep.  My best estimate of the time would be 9:30pm.
As we were talking, I noticed three non-blinking lights in the sky, in an equilateral triangle shape and traveling West to East (paralleling the islands length).  It was just off the South shore and about 400 feet above us.  I believe it was about midway in size to a small plane and a 747.  It made no noise.  The lights were not overly bright.  They may have been amber or a dim white.  I could see no stars within the triangle shape defined by the three points.  It appeared to be moving slower (perhaps by as much as half) the speed of a conventional aircraft.
I directed my brothers attention to it but I don't think he paid much attention since he was immersed in his conversation.  When I asked him about it a few years ago, he didn't remember it.  I'm not surprised, because it wasn't a spectacular event, just curious.
Witness indicates that the date of the sighting is approximate.  PD