I think you're saying that in the latter stages of Form 1 mufflers were required? I thought that was what happened but I have no real history of the event. This engine would be consistent with that change, but not sure why the carb.

If it was an FAI engine I would not expect the carb, plus a full tuned pipe.

As I said in a recent email to someone, I am sure the engine was not designed to go slowly and it ought to be fun for something.