It's interesting to note that the shoulder seam really has to extend straight out from the neck with no slope at all or the gown won't hang and drape correctly. You can see this in the diagrams of the original, but now I understand exactly why it was cut that way. That perpendicular line is part of what makes the nice folds coming from the shoulders. Cool, huh?
One other key thing I have learned is that the triangular gores really need to be blunted at the top so that they finish with a bit of width, rather than tapering to a point. Again, you can see this on the original but it wasn't at all clear to me why this was so until I put the back together and everything came to a neat point. I ended up without much of a neck opening. Totally fixable, but the the next time around I will cut my triangles with a 1 1/2 straightened off end, and sew all the triangles together before I attach them to the shoulder and center sections (I did this for the front and it went much better). I ended up losing a little length though, which means I have to do a bound edge for my hem. This is fine, you can see something similar in lots of the artwork where it looks like the fur lining is pulled around the hem of the gown.
Since I took the pictures, I shaped the neck and armscyes, and put in a facing/lining for the top section and sewed the shoulders. I am ready to sew the side seams, put in the sleeves and make the collar and cuffs. My dress form in an antique and has kind of funky shoulders, so I'm having a hard time getting a good picture of what it look likes now (the dress keeps collapsing into the adjustable part of the shoulders on the form).
I've found a bit of new inspiration as well in the form of the Seven Sacraments Altarpiece by Rogier van der Weyden (the whole piece can be viewed here, there are quite a few wonderful houppelands in this particular alterpiece). You can see in the detail pictures below two more houppelands of the general type I like, with some variation in the sleeve - both are narrower in the cuff, but still generally straight (rather than the bag type sleeve seen in earlier decades). The lady in the turban-like hood with the book has the more transitional style collar with less pleating around the bust line, which is probably closer to what I'll end up with with this particular pattern.
The under-collar on the gold/brown gown is also quite interesting. In later artwork there is a very transperant partlet type tying worn under some of the gowns, but a placket also shows. This looks like it's either an under-gown or the precursor to the parlet. What's interesting to me anyway is that there's no hint of a fitted gown (unlike the lady in the blue) or a placket. So, either the white bit is covering the undergown, or something strange is going on under there. It seems more likely that the white bit would be covering the under-gown, given that the houppeland is fur lined and would be hard to clean, it seems like some sort of layer to keep body oils off the fur around the neck area would be a good idea. There seems to be a similar sort of under-collar/parlet on the blue gown as well but worn under the under-gown. I wonder if this is the chemise/smock or a separate partlet?