How far up the Mekong River or other rivers during the Vietnam War did PACVs (patrol air cushions) travel?

During the Vietnam War the United States used PACV's (Patrol Air Cushion Vehicle's) to patrol the rivers of South Vietnam. Did these PACV's go into Laos or Cambodia using the Mekong River or what was the operation range of these vehicles? Did these see lots of combat while patrolling the rivers and were these ever used for Search and Rescues of downed US pilots? Did these also Patrol along the Beaches of South Vietnam besides the rivers?

Also did the North have any PACV's and if so did they ever see combat with United States PACV's?