It looks as if it has Cooper ancestry - but it's not in The book
So, is it Norton engined?
On second thoughts I'm going to lock this one for you (until your next reply) as you are pretty close to a solution with your reply.
As I said above, the engine is not a Norton.
Despite not being in
The Book it is Cooper based.
I would describe the car as being the first xxx xxx car designed for the xxx formula