What vintage movie is this gym threesome scene from? And who are the porn stars?

This scene is from the film Eruption from 1976, the guy is Wynne Colburn, the woman standing is Susan Hart and the other is Carry Welton
Here are two links to the full movie, scene starts around minute 64:

https://www.eporner.com/video-i2lVh73Pam2/double-porn-indemnity-usa-1977-le
sllie-bovee-susan-hart/

https://www.adultdvdempire.com/1438115/eruption-porn-videos.html

This scene is from the film Eruption from 1976, the guy is Wynne Colburn, the woman standing is Susan Hart and the other is Carry Welton
Here are two links to the full movie, scene starts around minute 64:

https://www.eporner.com/video-i2lVh73Pam2/double-porn-indemnity-usa-1977-le
sllie-bovee-susan-hart/

https://www.adultdvdempire.com/1438115/eruption-porn-videos.html

Eruption part 3

Full video here: https://xhamster2.com/videos/eruption-pt-3-13915512

Scene starts at 25:44