Genuine will cost either $81 or $173 through Amayama depending on how long you're willing to wait. If you can pull off the hubs yourself and go to a shop to have them press off/on the bearings it won't cost very much at all.
43280-AA100 Is the part number.
Here's a write up if you're keen to diy it.
http://forums.nicoclub.com/rear-wheel-bearings-install-t363488.html
Nismo kit shows exactly what you need and what you need to modify, doesn't mean you gotta spend 12K on the kit but it does show you what you will need to do it incl. where on the shell you'll need to modify for clearance.
Zenitani still have that Stag for sale.
http://www.kurumaera...36&stock_id=192
Nismo offer a conversion kit
http://www.nismo.co.jp/en/products/competition/mission/getrag.html
Nope the build plate doesn't list the build date. The section your talking about literally translates to "Error Field" so not sure what it's supposed to be.
Tbh I wouldn't worry too much about the month. 1989 should do.
Why would you wait 3 months to import a non turbo auto 4 door 34? You wouldn't save any money and you wouldn't really end up with a significantly better car than anything already here.