Bottom bracket shell shot. Emailed pics to SOMEC - they have lost early serial # records, but say that this is early 1980s (I figured that out too) made of SL and Air tubing.

https://cimg2.ibsrv.net/gimg/bikefor...16012b524.jpeg

Hi there! Congratulations on the bike, enjoy every minute of it. You joined a somewhat small club and the bike is really nice. Yeah unfortunately Somec has no clue records about their early bikes. I've seen on forums when someone asked them like you so they went to the back and asked the guy who made these back then... :) We dont have to go to Giant to see that such is impossible these days. I guess by Bianchi or Colnago also couldnt do it anymore.
Oh and a friendly advise ride instead of cheking for more info on Somec... I gave the plague to a friend who just swore not to buy more bikes. So he ended up with 2 (almost 4 but it didnt epend on him just on a dishonest seller) more. :)

in the 70s Eddy thought DeRosa was the only maker whos work was up to Masi standards and could
supply the amount that he needed.he also chose DeRosa to help set up his factory. can't get a better
recomendation than that! I don't know anything about later decades.

Well, Eddy was more than happy to let Ernesto Colnago build his Hour Record bike and plenty of other bikes before that. (Eddy's bikes came from a number of builders.) Eddy let the Windsor folks slap stickers on it just before that famous high-altitude ride in Mexico City, which is kind of like Ferrari making you a special one-off supercar and letting someone put Corvette stickers on it. The resulting photos featured prominently in Windsor ads for several years thereafter, pissing off Colnago no end. That is at least part of the reason Eddy went with De Rosa after that.
[/pedantic history statement]