Wow, a treasure trove of information. I think the best bet is mine was/is an ST-300 perhaps built by a shop. I'm fairly sure that the components on the bike -- with the exception of the front wheel -- were those on it for the ensuing 34 or so years. The front wheel was obviously replaced at some time with a chromed steel wheel. Oddly enough, it sports Campy shift levers. The freewheel sports only five cogs. BTW, my serial is not 40, I just substituted an * for one of the digits. So it's a good bit higher than 40, but less than 1000.
I already have a couple of vintage c'dales, my '86 BL, and an '83 "crest", so I wasn't exactly on the hunt for another. But when I saw a poor ole Cannondale with its bars flipped up to - - - well, flipped up, and a price of $40 I could not resist rescuing it at once. Didn't suspect that it was a fairly early offering from C'dale 'till I got it home.
I'm just gonna deep clean it, replace the front wheel to one that matches the back and ride it occasionally. I'd like to present it (to myself) as a survivor, tho a very deep gouge in the finish on the top tube ain't pretty. Its 56cm (or so) frame is a bit small for me, but the days when I was a badass needing a perfectly fitting bike are a few decades behind me!
Lastly, it has 27" wheels and tires. None of my fine stock of semi-retired 700c tires will be of any use whatever. Got a couple of tires on the way!
Thanks for your thoughtful and on-point answer to my inquiry.