Well since you mention you're willing to put basically any neck that will work on Ive just completed such a project.
Japanese necks are 0.9mm wider than american ones at the heel, I don't know of any discrepancies on that.
Indeed duo sonic 2, musicmaster 2 and Bronco necks will work and there are a good few of those on ebay from time to time.
Jagmaster necks will also work but those are as rare as jagstang ones on ebay, only ever seen one.
I will also warn you to consider the condition of the neck, a vintage neck will gain you that 'i've got a vintage part' thing but will be older and so more in need of restoration or closer to the time it will need it, worn frets and nuts and fractures are the big thing to watch for here.
But apart from that they're all the same really, you can fit american necks to jap bodies (ive done it) but it will cost in labour.