Actually just writing that last post got me thinking…
I just did a bounce of the whole montage after setup of tracklist and marker points etc but before putting on any plugins. Bringing this into Metric A/B then makes everything work great. It syncs exactly to the Montage timeline. Level match works as well.This feels like a good work around for me at the moment. I little extra admin but relatively elegant solution. Works with Metric A/B in Master Section or Output of Montage. You could also use this to reference previous master versions as well when doing revisions.
Although not ideal as the client could change track order or mixes but for the most part I like it!