Go to the New York Public Library and look for John Allison papers and see if there are any finding aids online. The description of each box is what you see in the 2018 post above, but finding aids will have been created by archivists and will give more granular detail about the contents. Those are often online these days. (Often papers are housed but not processed; if there wasn't an endowment to support the collection the papers await a volunteer or student to start the work.)

If you don't find what you're looking for, take your best guess about where those might be in the collection and email the library with your request for information. If you're not sure how to go about it, ask your own local library if they will help you place the request.

Good luck with your research! Here are a couple of links to get you started.

https://digitalcollections.nypl.org/

https://www.nypl.org/research