Some trivia:

Battery so that taillight can stay lit for at least about 30 minutes with engine off wasn't required until 1970 in the US...  it was 1973 for turn signals in the US.

Traditionally these laws go by date of manufacture, not model year.. 

So if I follow what your saying right, you don't need a battery for a 68 or 69 bike?

Legally, no. 

But a good battery is a critical component of the original "balanced" system so unless you're swapping to a new system (i.e. VAPE) or floating grounds and/or adding modern electronic regulator/rectifiers then you need to keep the stock battery.

Knutco11 wrote: "Led lights are probably not the best answer for these old bikes. Unsure if know but you NEED DC power to operate an led light."

Actually that's not correct, until recently I had a 6 volt AC LED fitted to both of my CT1s.
I only changed them out because the lamp didn't stand up to off road use and the end lens fell off taking part of the LED with it.
They were certainly bright and the beam was acceptable, if not perfect.

Can't attach a link to the LED lamp but it's eBay item number:254959285296.

 

254959285296 for sale | eBay

Some led lights come with a built in rectifier, a single diode sometimes. That will give you half of your output, if not already rectified. But led lights will come to life on ac power, even without a rectifier. What is an led? A light emitting "diode." What is actually happening is your using one of the leds as a rectifier. It will work for a while, but eventually will start burning them up. And only at half capacity, because even then, its still only using a single diode, so half wave.
Just trying to get ya some bright lights, and helps to know what your working with.

Leds are flooding the market, and are marketed for things they shouldn't be, imo.  My last example, I helped a kid get a yamaha banshee going.  One of the last details I helped with, he got some aftermarket led lights for it.  Plug and play and all.  Guess what?  They barely lit up enough to see a foot in front of ya at night, and they started burning out slowly.  No rectifier on a yamaha banshee, just ac output like a snowmobile or one of these old bikes.  Put regular filament bulbs back on, now it lights up the road like it should.  Leds are a Chinese scam like a bunch of other crap these days.  There ya go, my 2 cents.  Sorry for the rant, lol.

I looked at that bulb quick, and I wonder if it has a full bridge rectifier built into it?  I see in the description it says both positive and negative ground systems, as well as ac.  Those rectifiers are cheap, less than a dollar last I checked.  A quick way to find out, if the light works both ways on a 6 volt battery, it likely does.

After thinking about this I decided to try the correct bulbs before I change anything. I had forgotten that years ago when I first started working on my bike to get it back on the road it had a bad headlight bulb. I didn’t want to deal with finding the correct bulb at the time so I got creative. I took the old bulb and broke it apart and turned it into an 1157 socket and put a VW bug 6 volt dual filament tail light bulb in. It worked enough to get by. Now I am remembering that I have never actually tried the correct bulb. 
So I figured I’d give the Yamaha engineers their due and go completely stock before I try to make any changes. 

Just make sure it has a voltage regulator, if the 6v battery isn't wired in with all the lights working.  I wanna say you can get away with 12 volt on the oem yamaha headlight, but try at your own risk.