Richard "Grass" Green was a Big Name Fan in the beginnings of super-hero fandom in the 1960s. He was one of the major fanzine writer-artists; his signature feature was "Xal-Kor, the Human Cat." But he also did some pro work: in the 70s, for the undergrounds, but in the 60s, some work for Charlton. There he did humorous strips such as "Bestest League of America" in Go-Go and "The Shape" in the first issue of Charlton Premiere (September 1967). I believe the inker "Mac" would be Frank McLaughlin, and the "Friends" would be creator, designer, and plotter Roy Thomas (who had, by the way, originated the "Bestest League" in the fanzine Alter Ego).
Grass Green also ghosted the script and pencils on "Sinistro, Boy Fiend," in Charlton Premiere 3 (January 1968). The splash page credit read: "Art by Henry Scarpelli," and if I haven't missed it this time, he's the only creator who's been connected with the issue since.
I've only seen Scarpelli's pencils on teen features where he was emulating Stan Goldberg's style, but I can't see why he'd try to imitate Green's style here. The writing as well as the penciling style are Green's. Notice, for one thing, the reference to "It's a bird, it's a plane" in both features.