Yes, I'm still working on that. But I decided I need pictures on here, to demonstrate. Last time I took a photo of it it was what, 2 inches long? So. Here's a bad photo of the nearly complete but unblocked jumper:
All well and good, even up to the re-knit v. Don't know if you can see it, but the saxon braid splits into two plain old cables, and these continue up the side of the v. It's up over the shoulders and round the back that's been causing me issues.
So, a photo of my current solution, which may even be working: 
What this shows is the collar lying nice and flat against my shoulder, which is as it should be. What I have done is to complete the main section, and now I'm busy knitting up the collar, which I shall sew on. Cheating, maybe. If it works, I don't really care!