I think those are Nervex Serie Legere lugs with bilaminate for the spearpoint (I think that's how they
did that). Fairly common procedure on old british bikes, viking, claude butler and gillot all used this
technique.
I really think you need to contact Hillary Stone (he's a member here, same username) or
Norris Lockley on Classic Rendezvous List about this one, as they are authorities on British bikes.
The other group you might contact is http://www.classiclightweights.co.uk/index.html

Marty