Time to compare the original covers of Marvel Comics with the reprint book covers, looking for any changes that were made!
This time around, we begin with The Avengers #22 and the reprint in Marvel Triple Action #16. At first glance, there doesn't appear to be any real differences... I mean, we've got the floating heads below removed and replaced with a reworked title blurb, but look a bit closer... the art appears to have been slightly reduced, with ore of it appearing on the right side (although it could well be that the original Avengers cover got cut off in the scan). I'm guessing that when this was photostatted for the reprint, some of the burst lines around the Enchantress bled together, so the background got altered to be black. Apparently the Zip-A-Tone originally applied to Power Man was able to be removed, or it was a gray added in the coloring.
Sometimes, changes made doen't seem to make any sense at all. Take a look at the cover to Tales to Astonish #88 and the reprinted version in Marvel Super-Heroes #43. The figure of Namor has been entirely redrawn, so that he's no longer wearing his cape. It appears to be the same basic position, with slight changes. The robot behind Attuma has not only been redrawn, it's almost entirely different (the head is completely changed). Given that Attuma is about all that wasn't changed (even the water in the background has had alterations), I'm amazed an all-new cover wasn't commissioned! Also note the inserted picture of the Hulk -- since his show was on TV at the time, Marvel wasn't about to miss an opportunity to picture him on the cover, even though he has nothing to do with the cover story!
Not too much appears to have been changed when Amazing Spider-Man #138 was reprinted in Marvel Tales #115. The image has been shifted up, Spidey's thought balloon has been reworked, and the title blurb has been reworked to accommodate the UPC code. This is one of the rare instances where I actually like the coloring done on the reprint more than the original!
I have no idea why, when Journey into Mystery #120 was reprinted in Special Marvel Edition #2, an entirely new cover was commissioned (I'm guessing it was by one of the Buscemas, probably Sal... Absorbing Man's face looks very Sal-like). Don't get me wrong, I love Sal's work, but dammit, that Kirby cover was great, especially as colored on the original!
Next, it's Incredible Hulk #126 and the reprint in Marvel Super-Heroes #78. No big changes here, other than the burst and blurb inside it being relocated to make space for the UPC code. Better coloring on the original.
Here's another instance where a new cover was commissioned, when Fantastic Four #53 was reprinted in Marvel's Greatest Comics #40. Now, I loves me some Gil Kane art, but that original Kirby Kover was way better! I wonder... was the reprint published around the time the 1970s King Kong came out, and someone figured Klaw's solid sound giant ape would get more sales? Or was it maybe another one of those "If we put a new cover on it, someone won't figure it's a reprint" things?
This cover here, when Captain America #108 was reprinted in Marvel Super Action #10, shows that Kirby Kovers really can't be beat! This cover has all the action and power that you needed, and the only changes were shifting it down, correcting the coloring on the Trapster's sleeves, and making the title blurb larger.