The testimony of Anne Goodpasture concludes that the audio tape voices in MC were indeed a match for Oswald's voice despite no photos of Oswald existing. It's a large document but the last 10 or 20 pages home in on the conclusion.
http://www.archives.gov/files/research/jfk/releases/180-10110-10029.pdf
Where exactly does she say this? You can give a specific page and quote her on the matter.
From my reading, Goodpasture says that the CIA translator/transcriber of the calls - Boris Tarasoff - did a voice comparison of the two phone calls that Oswald made and said the voice was the same. But he didn't know the voice was Oswald's.
And it wasn't any sort of technical comparison. He didn't compare the voice to an actual tape of Oswald's voice. He just said the same person - he didn't know who it was at the time - made the two calls. One to the Soviet Embassy on September 28, 1963 and another on October 1, 1963. I believe it was these two calls that he said were made by the same person.
Here's the key passage, pg. 138:
Goodpasture: "The way it was used [the voice comparison], to me it would also mean that a person who had listened to two tapes at different times and said they were the same, that it would be a comparison by him.
Mr. Dodd: That was considered a bona fide voice comparison?
Goodpasture: Not in the technical sense that you are referring to. You are correct...
Goodpasture: A better way to explain it wold have been, probably, if this occurred, would have been to have said that the transcriber who listened to both tapes said that it was the same person rather than using the terim "voice comparison."
In his testimony to the HSCA this is exactly what Tarasoff said he did. He just identified the caller on the two calls as the same person.
FWIW, the Lopez report concluded that Oswald did go to Mexico City but may have been impersonated when he was there.
That report is here:
https://www.history-matters.com/archive/contents/hsca/contents_hsca_lopezrpt_2003.htm