As normal, more answers have resulted in more questions!
Waznot, can you tell what gearbox your car has, and if there is any rod system coming from the diff to act as torque reaction?
The Billington car, according to my contact who was close to the Northland Club and took many photos had an "Elfo" overhead valve conversion. The chassis didn't ring any bells, but for lack of knowing rather than anything else. Number plate position is right, but most cars had them in a similar place. For me , right now, your car is still possible Billington, depending on the answers to the questions above, as that car has disappeared. Engine change is always possible, for me that doesn't exclude it.
The pale blue car with the bonnet scoop is still a mystery, as is the venue. He has said the Northland Club didn't put out haybales at any event he knew of.