You posed the question so long ago, you may have figured this all out.
I'm not sure what the question regarding the rectifier is. It bolts to the frame and the two leads connect to the wiring harness, one goes to the battery, the other to the charging coil through the harness.
The instrument light bulbs are identified as T-3ΒΌ, BA9S, or miniature base, instrument bulbs. The BS90 is a 6volt system. Search online for miniature 6 volt instrument bulbs. The equivalent 12V is 1893, 44 or 47 bulb for the 12 volt bikes. The differences in the different numbers are different wattage or different glass bulb shape. There are about a 1000 different listings for LED versions of the 12 V bulb, they may work on the 6 volt system, but at reduced brightness.
The 1154 bulbs for the taillight are available in some auto parts stores, or online, you just have to look around. Don't use the 1157 12V bulbs, you don't want a dim taillight or brake light when riding.
Regarding coils, one is the ignition coil and one end connects to the points, the other is the lighting coil. You can find info in the service or technical manuals on this site.