As Dave notes, Angel was swapped out for Gladiator in one panel. If you look at the original issue, the Angel art looks like it was a quick-and-dirty modification. Since the original art was apparently modified to replace Gladiator with Angel, it seems that THE UNTOLD STORY version again had to be modified to put Gladiator back in.

As for the dialogue, it seems very clear to me that THE UNTOLD STORY features the original scripting. In each scene featuring the X-Men preparing for the battle, they all think about themselves and the possibility that they may not survive. In the final version of # 137, they are instead thinking about whether or not they actually should be fighting to save Jean. This seems like a logical change to make, in terms of stepping up the drama, given the revised ending where Jean commits suicide. Having each X-Man question if Jean deserves to live and then choosing to fight for her heightens the tragedy when she later makes the choice to end her own life for the sake of the universe. 

The UNTOLD STORY dialogue in those scenes feels like a step backwards. It’s less impactful, less on-point. Like watching the rough cut of a movie, compared to the refined final product. An interesting look at a reconstruction of the story’s original intent.

I could be wrong, of course, but that’s the impression I get.

ITEM: Let's tread lightly with DCCP #s 26 - 29. All written by Marv Wolfman and drawn by Jim Starlin, these were, in a very realistic sense, horrible stories about how Superman is so overconfident that he thinks he can beat anything by himself... which, it turns out, he can't. The Spectre team-up, in particular, is pretty heavy handed.

ITEM: Brian H., regarding "Phoenix: The Untold Story", I agree with you 100% about the dialogue being replaced by Claremont. And it did not improve the story. It feels like the Cyclops/Storm scene in the Savage Land... it got all twisted up.

ITEM: A few of the Marvel Essentials (especially Avengers and Fantastic Four) were far from consistent in the tone, resolution, etc. of the originals. Hell, some of the original product was double printed, as if there were a millimeter or two difference  I know these were cheap collections... but why not make them as quality as possible? Again, an editor reading the final copy to print could have fixed this.

ITEM: The biggest revisions to reprints that I can recall are the DC reprints - especially those titles in Mort Weisinger's stable. I can remember easily a dozen cases where "x-ray vision" was whited out, to be replaced with "heat vision." There were a lot of other replacements, depending on how much the mythos had changed since the original story was printed. And the lettering was so very obviously redone, it looked as if someone hadn't even tried (E. Nelson Bridewell?)

Further, I have several reprints of Superboy #147 - "The Legion of Super-Heroes." I have seen this with the last page removed, with the coloring of the Legionnaires' costumes changed, and even with the names removed from the front of their costumes.