Q: Looking for a parody titled “I’ll Sing on Your Album If You Sing on Mine”. I think it featured Willie Nelson and another CW singer and would’ve been from the ’70s.
A: This was a printed song-parody, not a recorded one. It appeared in the ‘Texas Supplement’, which ran (for some reason) in the Dec. ’77 (Christmas in December) issue. (Thanks to Natalie for providing the answer. More info in the Comments link.)