Vintage well-made porn: 'Insatiable' (1980) with Marilyn Chambers and John Holmes and others

There is a very good blowjob starting around 18:15 but she doesn't swallow. She overhears another couple later where there is another great blowjob.

What can be seen as a major fault in the movie is there is no clear instance of Marilyn climaxing. She comes close, particularly in the final scenes where three men and a women pleasure her in the mental sexual fantasy she is masturbating to. Which is the point of this movie, she gets lots of sex but doesn't get satisfied even in her imigination.

Multiple Orgasms for Guys

Passionate sex

Good advice on how to learn to have multiple orgasms

What if nothing happens? That’s fine! The point isn’t to tally up as many points (read: orgasms) as possible. The point is pleasure.
As O’Reilly says, “Experimenting with new techniques and approaches can be fun, but don’t get hung up on counting your orgasms!”

The bottom line The process of learning whether you or a partner can have — and potentially having! — multiple orgasms can be incredibly pleasure-filled.
Even if you don’t have an orgasm — or “only” have one — chances are you’ll be making some “oohs” and “ahhs” and “oh-so-goods” along the way.

https://www.healthline.com/health/healthy-sex/how-to-have-multiple-orgasms#positions