Pure speculation, but....

Assuming the Club seats have a better yield than economy (durrrrr....) wouldn't it be most likely that the planes they'll want to refit first will be the 38J ones, as these will go to 50-odd J?

This does mean that by trawling seatmaps (and looking for WT+ in zone 2) you should be able to see if it's a newly configured plane, so all we need now is a list of places where the 38J's fly on a regular basis.

I believe Toronto & Vancouver to start with...