Time once again to compare and contrast an original Marvel comic with the cover of the book reprinting the same issue! Most of this go-round's covers reprint the original covers with recoloring, but let's see if we can find any other changes!
First up is Fantastic Four #55 and the reprint in Marvel's Greatest Comics #42. Interesting to see how different coloring can make a cover look almost completely different, eh? The reprint is slightly reduced, and I'd imagine some minor addition had to be made on the right side as a result. The cover dress at the time required the blurb to be reworked, and as you can see it was cut and pasted into a different position. Note also that the speed lines for the Surfer have been altered above his arm to a broken line, instead of the original solid ones. The different coloring almost makes it look like the Thing was reinked, doesn't it?
Next, it's Sgt. Fury #63 and the reprint in issue #159, and the coloring is very different this time around. It looks like the art was reduced just a tiny bit, but other than that, I can't really see a major change.
There was a major reduction made when Avengers #76 was reprinted in Marvel Super Action #37... the art was reduced quite a bit to fit the larger cover dress, and the tower Arkon and the Scarlet Witch are on was cut off. Arkon's word balloon has been reworked, although it appears the original lettering was cut and pasted into its new position! The recoloring doesn't seem as extensive as on other covers, other than the Black Panther.
It may have been the scanning of the cover of Marvel Tales #135 that makes it appear so much darker than Amazing Spider-Man #158. Other than that, we've got a reduced cover and probably some added art on the left. It's also been shifted down slightly.
Recoloring only, plus Steranko's signature moved, when Captain America #111 was reprinted in Marvel Super Action #13. It almost looks like it was rotated slightly, but that could be an optical illusion (Cap's shield seems to be oriented just slightly different).
It was all-new cover time when Avengers #27 was reprinted in Marvel Triple Action #21. Note that the Witch's costume is colored much more red than the original purplish tones. It's odd that the new cover would resemble the original so closely... and how can you beat a Kirby Kover, really?
When The Incredible Hulk #122 was reprinted in Marvel Super-Heroes #74, it looks light a slight reduction was made, and the cover shifted down about a quarter of an inch or so. Note also that the blurb was moved to accommodate the UPC code. I think the coloring on the original was much better, the Hulk shouldn't be so brightly colored!
Lastly, we have Amazing Spider-Man #69 and the reprint in Marvel Tales #52. This is another shift-it-down-and-recolor-it-with-added-balloons job, like we've seen before. I remember buying this issue of Marvel Tales off the newsstand (probably the MTA issue a few covers up, too).