Hi Bob,
Re the top bit with the bronze welding: I reckon not Douglas, but instead something incorporating the two ends of a 1910-14 FN single-cylinder inlet manifold. The pressed "nipple" on the engine end of the pipe was matched by a similar one of the exhaust pipe, and a bridge - with a recess for each nipple - tightened by a central bolt clamped both pipes to the ports. The screw-in fitting at the other end was 1910-14 only (and maybe 1919 - not sure). I have an original manifold on the 1910 FN single, so don't need another. But happy to give it a home if it is lost.
Enjoy Wednesday - imagine visiting a shop after all this time! Before you know it we'll be able to cross the border and visit!
Cheers
Leon