Received some more information on the frame's early history. So a correction to the number of frames built, & who owned what / when.
1st the # built.
According to Denis there were 4 frames built (not 6 as I had previously thought). Two went to Ontario (he was in Vancouver at the time), one to Winnipeg (?), and one stayed in BC. It became a street bike, that got a 750 with a Piper prototype 8 valve head.
The frame for this bike was one of the two sent to Ontario in 1973. It was not however 'Robbie's 2nd frame', as I have now found out.
from Mike Crompton:
" The frame that was used for the 500 was purchased by Rick Andrews of Ontario Honda with the intention of putting a 750 in it. It was the mate to Robbies."
from Scott McKay in answer to my questions:
When did you guys build the bike? - "I believe the bike was built over the winter of 78/79."
Was it Robbie Meiklejohn's 2nd frame that was used? - "Robby never owned a second frame, Dennis Curtis built it (as I recall) at Rick Andrews' request."
That would seem to establish the when & for whom. Still trying to find out how Wayne McLelland end up building it at Ontario Honda. Also looking to track down more photos. I'm also working on gathering more of the bike's later history.