I'm reposting this to bring it to the current page of this thread.  As JB noted, it was from a calendar, the Decembe1978 image from the Mighty Marvel Comics Calendar from that year.  All seven Mighty Marvel Comics Calendars that were produced from 1975-1981 are included in the Mighty Marvel Calendar Book: A Visual History, written by "Capricious" Chris Ryall.  Commentary for this image:  "To close out the year, the December image was drawn by another relative Marvel newcomer who was already making a huge mark on their comics: John Byrne.  Byrne's offering exceeded all other calendar contributions in terms of the number of characters included in a single image: in this case, sixty in all! Longtime Marvel inker Joe Sinnott ensured stylistic consistency across all five dozen characters, and the image serves as a perfect capper to not only the yearlong celebration of Spider-Man, but also as the calendar's one visual reminder of the wide array of costumed characters present in the 1978 Marvel Universe." 

Spider-Man was the theme for 1978, which is why Spider-Man is so prominent in the image.  Some bonus material is also included in the book.  David Anthony Kraft gave instructions to JB to strive for a spectacular Steranko-ish poster pin-up effect.  Kraft also gave a list of characters to include, divided into four groups by approximate order of prominence.  The first, most prominent group included Human Torch, Thing, Hulk, Thor, Iron Man, Dr. Strange, and Howard the Duck.  Interestingly, the Punisher was included in the second group and Dr. Doom was included in the third group. I'm guessing they were included among this grouping of heroes because Dr. Doom was a headliner in Super Villain Team-Up and the Punisher had headlined stories in a couple of Marvel magazines.  This 1978 calendar would have gone on sale before the end of 1977, when the Punisher was still mostly just a Spider-Man villain.  

I still prefer the sleekness and anatomy in the original pencils, but at least here Palmer's ink and tone work is better able to (no pun, swear) shine.

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David Anthony Kraft, who was the writer for the 1978 calendar, sent you the following instructions:

"Include Spidey in central position. Strive for a spectacular Steranko-ish poster pin-up effect.  A knockout to finish up 1978! Above listing is characters in approximate order of prominence."

The listing referred to includes the following characters:

Group 1:  Human Torch, Thing, Hulk, Thor, Iron Man, Dr. Strange, Howard the Duck

Group 2:  Shang-Chi, Punisher, Warlock, Captain America & Falcon, Black Panther, Daredevil, Hercules, Ka-Zar, Ghost Rider, Ms. Marvel, Power Man

Group 3:  Man-Thing, Vision, Werewolf, Sub-Mariner, Captain Marvel, Mr. Fantastic, Iron Fist, Son of Satan, Dr. Doom, Killraven, Deathlok, Nighthawk, Valkyrie, Shanna, Nova

Group 4:  Old & New X-Men, Cat, Inhumans & Lockjaw, Invisible Girl, Hawkeye, Brother Voodoo, Sons of the Tiger, Frankenstein Monster, Scarlet Witch, Moondragon, Spider-Woman, Quicksilver, Doc Savage, Omega, Nick Fury

There was also a separate page with four groups of villains listed but the idea of including them must have been scrapped since villains aren't included in the drawing other than the ones listed with the (mostly) heroes.  If you have a comp copy of Abrams' Marvel calendar book, these pages are shown in the bonus material section in the back of the book.