This cover has a neat oval 4-digit Secteur Postal 4736 handstamp and would have made a nice inclusion in the presentation I gave at NAPEX last year. This is an example of a transitional marking with French text but that includes a 4-digit Vietnamese Khu Buu Chinh zone number. Note the use of the KBC abbreviation in the address line. The recipient appears to have been at KBC 3011, the Vietnamese Air Force general headquarters in Tan Son Nhut.
Speaking of NAPEX, I am looking forward to seeing everyone at the Society of Indo-china Philatelists annual meeting in McLean, VA next Saturday.