With a red line at 8 1/2k and only a neutral light I'd guess it's off a 1970 AT1 but one of the experts will probably prove me wrong.
6 1/2k redline on the RT1-B.
Looks good, what are the forks like under the gators?

Yep I agree with rt-1 pete. Dump the tach and get the correct one and red line will be 6500 with a single amber lense for the flasher indicators. That's the only light on the tach besides the backlight. The harness for the tach will only have those two bulbs on it.

Bike looks nice. You're onto it with he photos, no stopping you now & look forward to more in the future.

Neither of the forks are pitted, although one does have a few blemishes. Nothing that effects the seals.

Looks like I'm going to be looking for a replacment tacho, but I'm not going to sweat it. I'll just keep looking and see if anything comes up. Also, as I'm doing the wiring, if you take a look at the photo of my tacho you will see the ignition switch, which has three poitions. Left is off, middle is ignition and right is......I cannot work out if this is the lighting position as the back light comes on. I know there is a problem with the front lights as there is no live feed from the ignition to the headlamp bowl. If the right hand position is indeed the lights on position and not just the parking position I can slave off the back light feed for the headlight. Anyone?

If it is the same as the 1972 RT2 etc, then headlight only works with engine running (and key in last position).

Have I mentioned 6v regulator yet? Best to fit one to save headlight blowing (see Service Bulletin in Tech Library for more details).

You see, it's little snippetts of info like this that can show a fault is not a fault, but a quirk of the bike. Sadly, I'm not sure if the RT1 is the same as the RT2, but I can try it.

As usual Alan is correct, the headlight will only work with the engine running and fitting a voltage regulator will ensure it doesn't blow.
I saw your bike listed on eBay, I guess that's where you got it from. I saw a couple of videos of it running and it sounded like the revs were hanging on a little after the guy reved it. My RT1 does that when it's warmed up and makes me think I might have an air leak. I haven't got around to putting a leak test on it yet.

You might check with DEET and see if the face plate can be swapped for one without  the neutral light and with the correct redline?

He might make one that can be swapped in...  could be cheaper than trying to find a new instrument.

I wouldn't disagree with Mark (I never do!) but, if you are a patient chap, you could search through all used Yamaha tachos on fleabay and fleabay.com and see if someone has listed the correct one, but for a different bike. You can pick up some bargains this way.