I looked at a couple of dealer websites. One, in particular, had 53 pieces up six months ago and seven now. The only 60s page left is one Kirby is only credited with “finishes” on.
The dirty little open secret for the last few decades is that it’s very likely a lot of Kirby’s art in the open market was effectively stolen. There are stories of stacks of pages just disappearing from the office.
If you own a page of Kirby art from Marvel in the 60s, how sure are you that what you own was legitimately sourced? How do you know the dealer you bought it from — even if it was 30 years ago — got it through legitimate means?
Would you want to give that page up? Would you want to get served a letter from Disney/Marvel legal? Even if you have the paperwork from where you bought it, how do you know that guy you bought it from got it through legitimate means?
Might be a good idea to hide the fact from the public that you own it. Take it down off the internet, keep it in your portfolio or hung framed on your wall, and never boast about it again.