I actually just got a copy of the very hard to find book "Cassiar" by Suzanne LeBlanc yesterday. She says that the highway was completed in 1972, but I can assure you that I was not able to get through in the summer of '75.
Thanks for the comments, Joe. Yes, I still have an aunt living in Telegraph Creek - she spent more than 50 years at a remote ranch 25 or so miles downriver from Telegraph. The road in from the Stewart-Cassiar is a superb adventure, but is for small vehicles only (even a 30-foot C would make it a nail-biting trip for a few miles). When Billy Connolly filmed "Journey to the Edge of the World", I was his guide for a few days in that region. To say that he was wonderful to work with is an understatement - I still find
the trailer on Youtube exciting (my aunt Nancy is at 3:24).