Oh wow! That does sound like the guy. I wouldn't be surprised if Sandy Frank had some other actors that came and went during the production. The fact their credits were so paltry after episode 1 is really a shame, especially with the age of the dub making it more difficult if they hadn't kept regular records of who was in recording sessions.
His connection with Dinehart would make sense too, so yeah. I hope others might look into that! I made an attempt to catalog some BOTP/Gatchaman characters in a TV Request thread a long time back, but I needed express sources, which are difficult for those older dubs.
I still want to look into what episodes/characters Takayo Fischer may have voiced in, but hopefully with all these deductions, we might have a bit more of a cast and findings to present for a page

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So far, it looks like we have Alan Oppenheimer, David Joliffe, Takayo Fischer, William Woodson, Wendy Young, and now possibly Michael Rye to take into account for extras' voices.