This is the beginning of the legendary 5-year Kirby/Sinnott run on FF: Fantastic Four # 44 (Nov 1965). The cover was inked by Vince Colletta.
Unfortunately I don’t have scans from the original first publishing of this book, so I have to use scans from the Masterworks reprints which sadly lose quite a bit of detail since the source for these images are inferior stats and the coloring on this material is at times pretty bad.
The original printed material of this art blows this stuff away, but I think you can see here that Jack and Joe have produced some very solid artwork here, although I do think it takes a little while for the two of them to really mesh.
One thing is for sure, this work is a huge step forward from the Kirby/Colletta FF which was in my opinion, pretty awful. It looked like Vinnie inked FF # 41 over the course of a weekend. Watching how Vinnie handed the Torch’s flame is painful.
Here are a few samples from that book. To me I think the inking on FF from Colletta to Sinnott is like going from night to day, but everyone’s opinion will vary. Notice especially pages 5 and 11. No backgrounds!! That’s about to change in the Kirby/Sinnott run.