The tag was removed when the frame was repainted most likely. The frame number you listed is a K0 frame from 1970, so it has the correct geometry, but didn't come with that engine. Its not a 71. Dunno where they got that!
A few notes from the pics:
1. Pretty bike! Not original, but someone put some time and thought into it.
2. The top triple tree, your carbs, airbox, side covers, right hand controls, seat, rear fender, fork ears, exhaust, headlight bucket, engine paint, front fender, wheel paint and probably a few other things have been modified, are missing or are not correct for a sandcast. Thats ok of course. If you care about that stuff, you can track everything down from eBay, Yamiya or your local Honda Dealer.
3. Check the inside of your tank to see if it is a wrinkle tank.
4. Check the rear rim to see if it is a rolled rim (perfectly round sides).
Find yourself a Honda manual for the bike. Don't go with one of the 3rd party manuals. You can google for a wiring diagram.
On the neutral light (I assume you have checked your fuses), check the connections under the engine and to the harness. Then check the bulb. If all of these are ok, check continuity of the wire. If that checks out, then you need a new neutral switch. I suspect it is a fuse or bad connection.