[Arran]

I have the exact same model and the top of the shoulders was not veneered. Mine will need some refinishing as well so over time I have collected many photos of this model off of the internet and eBay auctions. None of them were veneered on top of the shoulders. As far as I can tell what you have done to the shoulders is almost exactly as I've seen it in prime unrestored examples. The original color was most likely a solid dark toner.

I see that now since the edge has a bullnose/rounded over profile, normally if it were veneered it would have an edged profile to give it some seperation, before the green paint was stripped off it looked like it had such an edge. Even though brand Z sets have a rather impressive look it's a rather cheap cabinet design when you get right down to it, but at least they used real veneer for inlay unlike the dinoc crap they used on some of the later models.
As for how to get the cabinet apart I can't answer in this particular case but if it's fairly easy to get apart there should be some blocks with screws holding the major parts together, if not it means they used rabbet joints and glue blocks.
Regards
Arran