Time for another cornucopia of Marvel Comics covers juxtaposed with the covers of the comics they were reprinted in, along with my comments about what changes were made!
First up, it's Incredible Hulk #148 and the reprint from Marvel Super Heroes #97. There's not a whole lot of difference here, the reprint features the art slightly enlarged, with the blurb on the bottom shrunk to accommodate the UPC code box... but look again, behind the Hulk logos... you can see the background got altered, with the wreckage not being quite as tall in the reprint!
Next, we have Amazing Spider-Man #77 and the reprint in Marvel Tales #58. Looks like the art is slightly smaller here, with some art being added on the right side. In fact, I'd have to say quite a bit was added to the background, especially on the upper right quadrant. Note the differences in how the Torch's flames were colored on his body, as well as the Lizard's eye.
Next we have The Avengers #40 and the reprint in Marvel Triple Action #32. This had a major cut-and-paste job done on it, the whole thing is reduced, with the Wasp, Sub-Mariner and Hercules shifted over a bit, bursts added behind Namor, and the background slightly altered around Namor's feet as well. Looks like nearly all of Namor's right arm was redrawn to me.
Here we have Sgt. Fury #32 and the reprint in #134... as was often the case, there were a bunch of word balloons added to the reprint cover, but other than that, the blurb reduced and the coloring varied (I prefer the original myself), I don't see any changes.
Here's one of those things that I look at and ask, "Why?!?" The Incredible Hulk #102, and the reprint in Marvel Super-Heroes #56... and there was a new cover drawn that is very similar to the original one. Why was this done? As usual, my best guess is to make the Hulk's appearance more in line with the current book at the time. I like the original more myself, but maybe that's just me.
Here we have Amazing Spider-Man #80 and Marvel Tales #61's reprint of same. Slightly reduced, the title blurb moved and the burst removed, but other than that, I'm not spotting any other changes.
Finally, here's Tales To Astonish #93 and the reprint in Marvel Super-Heroes #48. I'm guessing a stat was used here, given the loss of fine detail, especially on the Hulk (it almost looks like someone did a tracing of the original art and inked it without the attention to detail, doesn't it?). It's shifted down a bit, the blurb was enlarged slightly, but that's all I can see.