seller says bulb is an h4 60/55 bulb. should be alright with my charging system right?
Mostly, depends on your riding style. The battery depletes at idle speeds, so it will drain faster and recharge will be slower when you rev the motor. No problem at cruise speeds. But, you spend lots of time idling a stop lights....
So, she'll work if you treat her right, the charging system is up to snuff and you wiring is in good shape.
One thing you should do is measure the voltage getting to your present headlamp under operation, and then immediately compare it to what the battery terminals read.
The stock headlight will be dim with only 10V getting to it. And while a higher wattage bulb will appear brighter, neither old or new bulb will be as bright as it should be with low voltage getting to it. These old bike have been known to lose quite a bit of voltage through the system due to resistive connectors and switch contacts in the path between battery and headlamp.
You might be quite surprised how bright the stock headlight is with full battery voltage getting to it.
Cheers,