I am a retired Army Master Sergeant who worked in MACSOG Op-80 in 1969-70 and had a total of six years in Viet Nam from Jan66 - Aug70 with MACV J2 and Dec71- Jan73 with 1st Avn Bde.
Right now, I am a researcher and writer about the financial instruments of Southeast Asia with an emphasis on Viet Nam, Lao, Cambodia, Thailand and Myanmar.
Operation Benson Silk was not just a counterfeiting operation of NVN currency but one that counterfeited the first series of Ho Chi Minh Trail scrip.  There was another operation that counterfeited (on propaganda leaflets) regular DRVN (NVN) 1, 2 and 5 Dong notes but I do not know the name of it at this time. 
I hope you can use this information to update your Benson Silk entry.


Best regards, 


Howard A. Daniel III
The Southeast Asian Treasury