This is the cover art to RBCC #96 published in Dec 1972. It looks like the piece was originally intended for RBCC #74 (Sept 70 issue) as you can see light impressions of the pasted-on lettering that was removed! RBCC #74 ended up with a cover by Rich Corben so I understand why editor GB Love might use the Juanillo cover at a later date.
Bob Juanillo was a BNF artist of the late 60s & early 70s, contributing to many comic fanzines of the day. I first noticed his work when he provided the cover art to Rocket’s Blast Comicollector (RBCC) #’s 70 and 72, published in April and July 1969 respectively. He would also provide cover and interior art for such fanzines as ComicKazi (co-edited by Juanillo and Robert Napier), Collage, Comic Crusader, Destiny, Promethean Enterprises, Scream Door, This is Legend and Voice of Comicdom. A personal friend of Forest J Ackerman (Forry may have also been his agent), Juanillo was an artist for some of the pen & ink drawings for the Perry Rhodan paperback series. Juanillo was reportedly in poor health his whole life and died way too young at 30 years old in 1980.