Came across this on a Google Image search was being advertised by Honoroak Motorcycles in 2013. Sadly no frame or registration. Not the smartest Tri Greeves in fact looks a bit crude in places. Ad says its 1966 (which would maybe make it an East Coaster) but hubs are tin not alloy.
I have 2 EC's with 500 Triumph engines listed, frame number 25DC437B (GYL 390C) and 25DC440B (HJW 94D)
Could be one of those I suppose