Mystery solved.

Remember this? Hume Weir in 1976.

It's a long time ago and I was certain it was Trevor Jones' red one. Now note that distinctive bonnet scoop.
Then along came this picture of Alfredo's from Calder, same year.

Same scoop. The car's blue. Must be John Gourlay.
Peter G's Auto Action clipping from 1977 confirms it.

Here's John's car at AIR, same year. Still has all the holes in the nose but it looks like the ProdSports police have caught up with the bonnet scoop.

That's a young Ken Stratton in the yellow Bolwell t-shirt.