1661 HCU (Heavy Conversion Unit) was a training unit so he may have been there as an instructor.
The DFM recommendation was the statement made by a commanding officer in support of an award. In some cases these were printed in the London Gazette as citations, but not always. But these recommendations can be found in the National Archives and they have been collected into a book that I have.
PM me your email address and I shall send a scan later on today.
I would recommend that you request his service records as that will list all his postings from enlistment. To do so fill in and send the form on this site:
http://www.veterans-uk.info/service_records/service_records.htmlMake sure to request photocopies of the original files because otherwise they will send a typed summary that may omit useful info. If you need help in interpreting them when they arrive then do ask here.
K