So is this definitely a 1977 frame? I may have to concede the Benotto bar tape then....TBH I cannot remember... What year did that stuff first appear on the market? IIRC it can't have been much before '77, if at all.
I never even heard of a Cobra bottle cage before I read your post. After a trip over to Velobase, I can see that I would have had to have been a very sharp-eyed teenager to distinguish it from a T.A., in a photo of, say, Hennie Kuiper, 35 years ago. So, yeah, a Cobra if you prefer.. Save yourself another ounce! I seem to remember one called 'Emmepi', or something like that, as well. What year did the Elite cages appear?
Anyway, for all I know, the OP may be perfectly content with the existing cage. Also, the last thing I want to do is encourage anyone to pay inflated prices for obsolescent bicycle components.. A bottle cage was about a fiver in 1977, and that's about what I'd pay for the same one now... They can't be that