I done the conversion a couple of times before.
First of all, you have to be sure you've got the correct crank tap type on your engine.
This HAS to be a L-tap, so no taps with a 'flat' Hitachi flywheel fitted.
Next, the only reliable Chinese CDI ignition is the one from the early Jingcheng engines. (DX50, DX90)
This one is plug and play if you buy the special piece of the wire loom. No experience with the Ebay US versions.
It's possible to keep the 6v bulbs and batteries IF you manage to find a correct regulator.
Again, Chinese electronics are far from reliable, and thus I don't recommend them.
If you make the conversion, I'd suggest to do it right.
Get everything running on 12v (regulator, battery, bulbs,...) you won't regret it as it's a big improvement.
(Altough I keep my bike on an oldschool 6v myself)
What you could do is to search and fit in a Honda 6v CDI ignition, as used on f.e. Monkeys from Finland.
Very reliable, very good, but... very rare.
In short: Please don't make a partly conversion. You'll end up with unreliable Chinese parts, weak lights, blowing bulbs, and no-one will understand the adjusted wire loom for future maintenace...