It's unusual their unit isn't inscribed on the marker but that does occur. That's another item, however, that will be contained in the file - at the very least, their squadron will be listed. I have a reference on hand from which I can provide the group and numbered air force to which they were assigned or attached. Since I have all this on hand, there'll be no charge.
If you contacted PERSCOM in September, you should have received confirmation in October. It's anybody's guess as to when you'll receive the file. Once - a few years ago - it took nine months to receive a file in response to an "accelerated request" (I still wonder how long it may have taken had they not "accelerated" the request). They've improved somewhat - you might receive it as early as sometime within the next month.
Very Important!! Group burials result from inability of Graves Registration personnel to identify individual remains. Remember, these guys were in an aircraft that crashed - and probably burned - after falling from several thousand feet. Six men are listed on the grave marker because Graves Registration found body parts sufficient to suggest six individuals. Deceased files relating to group burials can be pretty graphic. Those who handle these files usually simply (1) pull the file, (2) feed it through an automatic copier and (3) send it out. There's usually little-to-no editing so be prepared for a shock - maybe a big one. It's not good, bad, right or wrong - it's just the way it is.