ARGH! So, the Queen Mary gown I'm starting on........back in the day, I did a *ton* on internets research on it. (Things happened, I got distracted by Italian, etc. etc.)
And now that I've come full circle, I can't find all the stuff I found the first time 'round. (Namely detailed Janet Arnold-esque construction details.)
Anyway, I've been looking for some portrait comparisons in the same-ish date range that have similar attributes:
All three have the extra-long sleeves, and the two on the right have the right neckline. I've not found anything that has the same type of chemise (or whatever it's called in this time and place), however. Total bummer.
ETA: Hold the phone! it's the wrong 'style' of gown, but here's one that has a blackworked underdealio (smock/chemise/camacia-y thing. Must find correct terminology so I don't continue to look like a total dweeb.)