Eric Edwards really delivers in a homoerotic scene where he is getting it on with a woman and they are joined by a woman who is dressed as a man. Eventually the woman whips out her strap on dildo and Eric Edwards and the other woman give it head. Then the woman uses her dildo on Eric Edwards butt. The movie is called "Midnight Desires" and was made in 1976. If you go from the 33 minute mark that is when things get interesting.
There is a thread over at The Datalounge where a poster writes that he talked to Eric Edwards about the scene and apparently Eric Edwards said it was real and he didn't have someone else stunt butt for him. Whether that poster is being truthful I don't know. Regardless it is a hot scene and Eric Edwards does such on the dildo so that is pushing the envelope as far as I am concerned. I think Eric Edwards was a good looking man and I appreciate his career in porn.