There is a list of B-29 losses during the Korean War time period here:
http://www.koreanwar-educator.org/to...ses_damage.htm
The description of the loss of 42-93974 would seem to rule it out.
Maybe one of the other crashes described would be a better fit.
Brady was in the 2nd Battalion, 7th Marine Regiment. There are on-line records that can be consulted, particularly if Brady's book would narrow the event down to a few months. I believe he was in Korea during the winter of 1951-1952. He arrived in November, 1951. I looked at a few of the months. There was a body recovery of a Marine (not an Airforce crewman) in December 1951. Possibly he has confused things? Other possibilities are that he has the date wrong or the event happened when his company was attached to a different battalion. (When you read through the on-line records, there are times when individual companies are temporarily attached to a different battalion. It would probably be necessary to read the other's battalion's reports during those times).
https://www.koreanwar.org/html/usmc_...it.html?pid=86
Here is the incident description from the book. Note Brady says the crash would have been seen for 10 miles up and down the front lines. Also, from my reading of it, it is not clear the Brady's unit recovered the airman, only that he had heard about it.
https://books.google.com/books?id=dO...20B-29&f=false