hello d-four,

good to read this report and see the photos. thank you for posting. you always seem to find the most fun items! bicycle looks like the oeglaend counterpart of the mcb (monark-crescent) model 305:



this example approximately 1973.

owned a 305 from right about this time. it was kitted very close to this example. one surprise: its briga chainset was wearing t.a. c/w's.

some years later purchased a badly crashed example for parts at a flea market. still have its briga chainset all together in the frame's bb. this set has an interesting design, it is one-piece yet mounts in a standard diameter bb shell.

the shade of green on your dbs seems to be almost a house colour for them. have seen it on several different models. owned a competition model from about 1967 that was this finish as well. it was eleven tube reynolds with nervex professional lugs. built with verot 55 chainset, huret gears, weinmann cp brakes, titan stem/bar set, atom 440 pedals. looked quite close to this 1971 beastie:



wrt to the odd fitting on the back side of your machine's head tube: the mcb 305 has something similar. theirs is a hole plugged with a grey rubbery vinyl square plug. have never known its intended purpose. could be for lubrication or it could be just a hole made to ease some step in the manufacturing process. it does not stand up away from the tube as yours does.

thank you again for sharing this new arrival.

best to you and to your mounts.