I believe Boeing 307 Stratoliners were still operating in Laos into the early 1970
Arrived in Tan Son Nhut airport Saigon September 1970 to see a pristine polished metal 307 on the tarmac, a number of them operated in the area apparently, one is noted as ditching in the Mekong River in March 1975 while on a flight from Hong Kong to Vientiane.