Thanks for this.
This hits the nail on the head right here. Monty wasn't sheltering his 4th line defensively. He felt comfortable using them against top players.
And consider this, the had this deployment of 4th line while still having arguably the best defensive forward duo of their generation in 37 and 63. Without Bergeron, the 4th line will likely get even more tough match-ups.
I'd start him on a line with Geekie in the middle and Boqvist on the other wing. Give them the softest defensive match-ups, especially early on while all 3 are getting used to Monty's system.