Strange Tales Annual # 1, 1963. Kirby pencils; Sol Brodsky inks?
I started out with this cover since I noticed the background, circular webbing motif is similar to the design on Avengers # 11. Stan Lee often designed covers with the artists, so this may be an instance where he decided to use the same idea on the Avengers cover a year or so later. As we can see here, there are a number of instances where Kirby differentiated from Ditko in his interpretation of Spider-Man. Spidey's webbing in not always drawn correctly, notably on the belt and the feet; the left foot in particular has lines that are completely wrong. The boots are smaller than Ditko's version, and the spider on the chest is noticeably absent. Kirby does draw the underarm webbing, and overall presents an acceptable Spider-Man.
Amazing Spider-Man # 10, Mar 1964. Kirby pencils on Spider-Man, Ayers inks?
This Kirby drawing of Spider-Man, which appeared a few months after the Strange Tales Annual, is interesting since it has Spidey in a side view. You'll notice that Kirby's Spidey face mask is flat, with no definition of a nose (or face underneath), as is noticeable when Ditko draws him. Here Kirby remembers to draw the spider on the chest (unless someone else added it), but he draws the ankles very thin, and the webbing on the glove that is pointing to the Enforcers has lines going all the way to the fingers. Interestingly, the glove holding the webbing has the lines on the fingers correct. It looks like Ditko may have fixed that hand, although why he didn't fix the other is a mystery.
Ditko Spidey - close up from the cover to Amazing # 21, Feb 1965
I thought it would be interesting to compare a Ditko Spider-Man figure/pose with Kirby's. As mentioned, Ditko's mask looks like it has a nose whenever there is a side view. Ditko's musculature is more realistic, and his webbing design is fluid. His Spider-Man looks thinner and younger, while Kirby's is bulky and stiff. There is quite a difference between the two interpretations.
Tales To Astonish # 57, July 1964. Kirby pencils; Sol Brodsky inks
One last cover worth noting. Here Spidey is swinging through the air on his web, which looks more like a net than the webbing Ditko draws. In every drawing I've seen, including the interior stories Kirby pencilled, Spidey never shoots his webbing with his index fingers as Ditko's version does: Kirby has Spidey making a fist when shooting his web. Once again, the webbing design on Spidey's costume is off, looking like a series of U's on his arm (the webbing also covers his entire arm). The spider on his back is also missing.
Noting the differences between Kirby and Ditko's versions is not meant in any way to denigrate Kirby, only to show how diametrically opposed they were in style. Ditko, for his part, had a very hard time drawing the Thing; his hard rocky exterior appeared to confuse Ditko's design sensibilities . Still, there were occasions where both men were able to do acceptable work on others characters. I always thought Ditko did a fine job on the Human Torch, while Kirby's Dr. Strange cover vignettes (which look like they were based on Ditko's interior scenes) and guest appearances, while not perfect, costume wise, had a charm of their own. Both mens individual imprints are unmistakable. That's one of the things that makes their art and storytelling endlessly interesting.