It is highly unlikely to be CV. CV was popular in the late-60s until about 1972, by which time EIAJ had pretty much supplanted it. The latest CV tape I have ever encountered was from 1971. EIAJ had so many advantages over CV that most people who had CV switched to EIAJ. It's hard for me to imagine anyone making a CV recording in 1977, but I have seen numerous EIAJ tapes from that time period. And anyone who for whatever crazy reason was still using a CV deck in the mid-70s, would likely have made the jump straight to VHS by 1977.

I also have a good CV deck and a myriad of time base correctors. Although in the highly unlikely event that this does turn out to be CV, and if it turns out to contain anything of interest, it would be advisable to try it on multiple CV decks. CV doesn't have tracking control, so different machines play and record with different tracking alignment. EIAJ allowed for tracking control. (Also, later-era EIAJ decks had onboard dropout compensation and other features that greatly improved picture quality)

Hard to imagine, but manufacturers of CV decks didn't include tracking control because they hadn't envisioned people wanting to play back tapes on a different machine!