To answer the second question: I looked up the reference I've copied from @mike65535, and it is as useful as a Callbook itself. I looked up my parents in the 1966 Callbook (k1uzg and k1uzk) and found their listing. I also looked up my original call (wa1jms) and found that I wasn't yet licensed.
The archive includes several years of the Callbook. Each contains scans of the original Callbook pages, organized like the Callbook: 0-land, 1-land, 2-land, etc, and then alphabetically by suffix.
The scan is at the lowest possible resolution and the scan is functional, although finding a call can be like pulling it out of a pileup. I accessed the archive with my cell phone and was helped by having a magnifier and squinting.
In an earlier comment I noted when I was retesting for my long-lapsed license, I needed to prove my previous license to avoid the code test. For the particular VE, a Callbook showing my call would have been sufficient proof. If I had this archive, I might have avoided taking a 5 wpm code test after 25 years of inactivity. Fortunately, the code was burned into my brain deeper than I thought, and 5 wpm is very slow.
I have just re-read my answer, and it isn't very helpful for your problem. You need to search by name, since you don't have your father's call. I focused on the wrong aspect of the question.
I would forget about the FCC database and concentrate on general "old-fashoned" Googling. Search for his name. If there are too many hits, add "radio", "amateur radio", or "ham radio". If you know his company, Google with that company name. Check if there is a radio club at the company -- many larger companies have clubs. Look for other hams in the area where he lived. The site shows all the currently licensed hams by area or zip code. Contact them and see if they know your old man. Maybe first contact the ones with old calls. You can use qrz.com to look up the local calls.
I wish you all the best finding information about him. Hams are a friendly lot with long memories. If he was a ham, you'll probably be able to find a thread to follow.