Neal started this cover in 1970 for Thor #180 but, according to Neal, Marie Severin had done a layout for the same book that Stan Lee asked Neal to follow. So Neal stopped working on this one and did the one Marie designed. Neal looked at the sketch lines on the cover and he said they indicated what direction he was going with it and he was happy to finish it in 2016.
At CAF, you can see the original 1970s cover with Odin, Thor and part of Mephisto. To finish, Neal completed Mephisto and added the demon. Again, per Neal, the layout was intended (and is) a split screen of 2 worlds. Thor is being cast out of Asgard into wherever Mephisto is.
As always, Neal and Jason were PHENOMENAL to work with. Neal is incredible and pours his heart out into his work -- I encourage everyone to get to his website and purchase your some of Neal's work for your own collection!
Hope you like this Neal Adams cover:
http://www.comicartfans.com/gallerypiece.asp?piece=1363838