I don't know if this was actually drawn for Charlton Comics and never used, or if it was a fanzine piece, but I thought it was pretty cool and wanted to share it here.
UPDATE: Apparently this art was misattributed by the site where I found it. It was actually drawn in the mid-80s by Gene's brother David Day and inked by his other brother, Dan:
My name is David Day, I am the youngest brother of Gene Day. I was 16 years old when my brother Gene passed away in 1982. I am also a professional artist with a 25 year career in the business. I have worked for Marvel, DC Comics on such characters as X-Men, Iron Man, Spider-Man, Hulk and Batman...but I am most remembered in comics for working on licensing.. such as Man From Uncle, Sherlock Holmes, Lost In Space, Quantum Leap, Mr T and The T-Force, Nightmare on Elm Street to name a few. I drew the Space 1999 piece above for Sword and Stone Publications who bought the rights from Charlton Comics Archives. It was not Gene that created that picture. I drew it and my brother Dan inked it...it was done in 1986... I was 20 years old. Nice to see that someone has found it... I do not even have a copy of it.My apologies for the mistake, and my thanks to David for clearing it up.
All the best,