I think the inking is too heavy to be Big John. His '80s self-inked work is of course very loose and wispy, but even the '70s examples have less weighty lines than this cover. I think it's the obvious Buscema pencil work on the faces that probably makes it scream Buscema, but I would bet that it was inked by someone else.
Regarding the GCD entry above, just as an FYI, the GCD often lists Morrie Kuramoto on the cover credits, but he was a letterer/production staffer and not one of the pencillers or inkers.
Yeah the GCD listing has Morrie listed as the letterer for this issue.