So I finally decided to make the top open at the back, which wasn't 'historically accurate', but sometimes ease of sewing, and the final look are more important (lesson learned from the coat). I stitched the striped neck insert onto the navy blue top, all the way around the neckline.
I designed it so the front 'points' would not come to a sharp point, but a little wider blunt one, so that I could better hide tiny snap fasteners under them. The collar is lined, sewn all the way around, leaving an opening at the back neckline, so it could be turned right side out. After clipping the corners and curves, and turning it right side out, I stitched the back opening closed, pressed the collar, sewed some wider silk ribbon under the points, for the ties to make into a bow, and sewed tiny black snaps at the collar points on top of the ribbon, and on the front of the top. I used black snaps so they'd not stand out against the navy blue. I thought it worked quite well...