Dear Jamie Mayhew,
Thank you for posting your request on History Hub!
Veteran pension files should be in the custody of the Department of Veterans Affairs if they were still active in 1955 when the inactive files were transferred to the National Archives. Because the veteran did not pass away until 1964, his pension file would have remained active until his death or the death of any surviving beneficiaries such as a widow.
Since both RDT1 and RL-SL have already informed you that they do not have the file, please file a FOIA request with the Department of Veterans Affairs. Their FOIA website is https://www.va.gov/foia/. All questions regarding VA’s FOIA procedures and fees may be emailed to VACOFOIAService@va.gov.
We hope this is helpful. Best of luck with your family research!