|Chicago History Museum|
Fortunately the zoom in feature given by the museum confirmed that impression.
This gown was remodeled. You can clearly see the fold lines on either side of the bodice front that used to be the robings. You can also see quite clearly where the box pleated decorations of the robings abruptly stops at the shoulder.
A more visible view of the box pleating and also of how the robings (which are now the shoulder straps) were once attached to the back pleats.
So what did it look like on the wedding date of 1770. My opine, it looked like it started out in life, a stomacher front open gown. Later typical (and rather clumsy) alterations bringing it up to snuff in the late 1770s or early 80s.