Have you tried the website classmates.com to look for William Cullen Bryant High School. Looks like it is also listed as William C. Bryant High School.
Good Luck in your search.
Dear Mr. Monaco,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located Classification 157 (Civil Unrest) Case Files, 1957 - 1978 in the Records of the Federal Bureau of Investigation (Record Group 65) that includes the file New York, [New York] - 157-681-v.1 [Classification - Civil Unrest] -- Threat to Bomb Bryant High School -- Queens. This file may have access restrictions which will require it to be requested under the Freedom of Information Act. For more information, please contact National Archives at College Park - Textual Reference (RDT2) via email at Archives2reference@nara.gov.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT2. We apologize for this inconvenience and appreciate your understanding and patience.
You may wish to contact the William Cullen Bryant High School, the New York City Department of Education, the New York City Municipal Archives, the New York Public Library, and the various New York City newspapers for possible records and photographs of the high school Also, some editions of newspapers through 1963 are available through the Library of Congress’s Chronicling America project.
We hope this information is helpful. Best of luck with your research!