Back in 1978 BCM lugs were in the US for fame builders. IIRC Cycle Imports (of Cornish MI) offered them along with Prugnat too. So, the presence of BCM lugs won't eliminate USA builders. What does, IMO, eliminate USA builders is the low grade of the joining prep. Pretty much any USA builder who would have used lugs back then would be a small job shop at the largest to a one man show at the smallest. I seriously doubt any of these shops would not do a better job of the tube miters.

I think one will find that many brands had BCM lugs.

French shells were also available here but rarely used. I have no specific memory of any USA built frames with French BBs but I'm sure there's a few out there. Very few. Andy

This is true, and I have never thought it was anything other than a factory built frame given the interior bb pics. I think the French shell would indicate France, mostly

Eric- I didn't think you thought otherwise. It is the OP that is questioning all this. Andy

You did say they would be better and I also have a different thread in C&V about this frame too. They're also as baffled as we are here but a different point of view has answered many of my questions that's informed the other thread. C&V thread

Of the frames from asia in this timeframe, what would be the companies that imported widly to Europe so the most likely to to have this bracket threading. Does this look at all like belgium to any of you?

I think that almost all Asian bikes have come with English BB shells. I think the French were perfectly happy to sell English threaded bb's. But it's certainly possible some company supplied French lugs/shells to an Asian company.

Do you have a way to measure tube diameters? I'm curious if it's metric tubing. What size seat post does it take?

The seatpost is 26mm (could easily be 26.2-26.5mm since I read that's a french standard back then) and the head tube is 30mm. I can get the rest in a bit.

I don't like to judge a tube's OD by its ID. Especially in bike making where seat tube reaming is a common step. The comment about the post size having a .5mm range suggests a poor ability to measure. The best way to determine a post size is with trying various sizes of posts. Since the top of the seat tube gets a lot of heat and often in two or more separate procedures the ID can, and often does, deform so a reaming can be needed to get the ID back to round enough to fit and hold tight a post. Sometimes a bit more reaming is needed and the post size is picked to fit that. It is not uncommon to have the ID at the top of the seat tube to be smaller than deeper in the ST, or better said the post that fits the top of the ST might not be the best fit further down the ST.

By a 30mm head tube I assume you mean the ID is that. This is a spec that the headset's press fit calls out. Again the after reaming ID has little to do with the OD. Remember for the same OD a bike tube can have different wall thicknesses. Andy

Sorry here are all the updated Tube diameters measured by the OD

TopTube 26mm
Down tube 28mm
seat tube 28mm (with a 26mm seatpost, Maybe not original but it fits well)
Headtube 30.2mm (The headset parts are all threaded french and the sterrer is 22mm)

Those are metric tube diameter, which were most common on French frames prior to the early 80s. Zeus (Spain) frames also used metric threads and diameters.

Thanks again for all your insight! As I've taken some space from obsessing about this I came across a Swiss brand I wasn't aware of previously. Do you have any info on a brand called Titan or Oria Tubing? I saw a handful of the bikes online that has some shocking similarities but couldn't find too much info on their history or catalogues.

Back in the beginning of motor vehicles (and air planes) many countries had their own steel processors and thus a "country" tube brand. For many reasons (politics, economics, war) some of these tubing brands survived and others went by the wayside. You might post this question in the C&V sub forum. Andy