I've found this mentioned in a number of places, but I haven't found an illustration of the claim. Here are the first lines of each panel's first balloon on the first three pages of CMA 1:
Joe Simon also testified at that trial, as he and Jack Kirby supplied the art. Part of his testimony included the fact that they worked from Fawcett's scripts—and despite that, to this day the writing of CMA 1 has been attributed in places like the DC Archives reprint to Simon.
The point of Wellman's testimony was that he was instructed to copy Superman. But that reads, in the retellings at least, as his being instructed to copy Superman before Fawcett ever first published Captain Marvel—his writing Captain Marvel Adventures 1 showing that he was "in on the beginning" of the character because, you know, #1. That Cap debuted in Whiz Comics a year earlier goes unmentioned.