Do whatever you want it's your car but you don't HAVE to do anything. Restored headlamps with stock bulbs are bright. There are 6v halogen bulbs if you want them.
There is no reason for the starter to spin faster unless you want to race her and you need that extra 1/2 sec to get off the starter block.
Add up the costs of all the parts you need to change over and the money out of your pocket for the 6v battery goes down.
But if you insist;
Battery
Any good 12 Volt battery will do as long as it will fit your battery box and hold down. Most seem to selected a 72 month, 675 cranking amp, universal battery.
Generator
A GM 63 Amp Alternator with an internal self exciting voltage regulator. The hook up is one wire, the same as the existing generator. You will need to make two small brackets to mount the alternator or you can use two shackle bars and drill out for the proper size bolts. An alternator pulley can be purchased from your friendly Model A parts supplier.
Starter
No modifications are necessary to the starter.
Ammeter
Changed the standard 20 amp ammeter to a 30 amp ammeter as an alternator will peg the standard meter. You must reverse the leads on the ammeter due to the change in polarity of the battery. Your neighborhood Model A parts supplier carries the 30 amp ammeter.
Headlights
You may want to convert to Halogen bulbs. The conversion is relatively easy. You can purchase a kit to modify your existing reflectors or you can purchase new reflectors with the Halogen sockets installed. You must install an alternator to successfully operate Halogen bulbs.
Ignition
You could install a 12 volt coil and a resistor to reduce the voltage to the points.
Or install an electronic ignition system. This is an extremely easy system to install as it fits entirely inside the distributor; no outside boxes are required. Kits are available for the standard Model A or B, early V8, and Mallory distributors. Both 6 and 12 kits are available.
Kits are furnished with a new coil as the correct coil resistance is very important for proper operation. Kits are distributed by: Remund Ignitions, Inc.
P.O. Box 857
Lemon Grove, CA 91946-0857
(619)460-3620
Horn
Getting the horn to work properly was the most perplexing part of the conversion. You can purchase a 0 to 2 Ohm variable power resistor with a 100 watt rating from an electronics supply house or the Model A vendors have part you can use.
An alternate approach would be to rewire the horn.
Light Bulbs
The following bulbs can be used with a 12 volt system: Cowl, Tail, and Dash Lights - #89, 6 cp
Dome Light - #67/97, 4 cp
Stop Lights - #1156/10, 32 cp
Turn Signals
If you have a Signal-Stat turn signal it will be necessary to change the flasher to a Signal-Stat #180 and the bulb to a #1445.