Perfect. "Then" means "at the time" as used here.

I can't remember what I said before, but Italki automatically erased it and banned me for it. Anyway, to cut a long story short, I said it was fine, but I would still make some subtle changes for clarity, attentiveness, etc. These changes included changing the first word to "This". And personally I would not make any of the changes suggested by other people here - I prefer the original and the main thing I would change is the first word.

I agree with Albert. The sentence is grammatically correct, but it needs some punctuation to make it more readable.

Yes, the sentence is correct! 🎉 It is clear, grammatically sound, and provides detailed information effectively. If you'd like a more concise version, you could say: "In 1980, Michael Stone generously donated the collection to the museum, thanks to the efforts of Stella Bush, then head of the Manuscript and Memoir Department." Both versions work well—your original is polished and professional!