Pat Boone and Peter Ronson are both hot looking and loose most of their clothes on the way down.
I actually found this on my own.
Johnny also has a nude rear shot in in the sex-caper comedy, The Great Texas Dynamite Chase 1976.
I painstakingly observe — it's a tough job, but someone's got to do it! Given the size of the dick in question, I'm not surprised he didn't mind showing it off.