I recently bought a CT2, which looks to be #1398 for 1972. Bike appears to be pretty original.
The swingarm has all the makings of a 71 model. Also I notice that the steering stem nut has
a hole drilled in it for what looks like a steering damper rod like the earlier bikes had. Wondering
if Yamaha was using up some left over pieces. The mounting for the shocks on the earlier swingarm
makes the shocks stand up straighter so I doubt it was something changed by one of the two previous
owners, The swingarm also has the bracket for the clip on the chain guard like the earlier bike. 
Thoughts?

Sounds like ya talking 250 with steering damper hole. With swing arm are you talking square as in early dt1 was. Or am I off the planet as usual. I'll go look on partzilla for changes. Ok 175 then, what was a s arm differences, shock mount further forward on the arm or something like that. I don't recal any 175 having a friction damper but my dt1 did in "69. I have a "70 125 with no damper. "71 is a 248 number & 72-3 is a 315 number. Maybe it's length or something. The bonded rubber steel 'never wear out" bushes are the same number but drawn with a different look but same really. Anyway, now I've confused things, have a good day.

Any pics via imgur or similar if possible please. Can't see them on what I'm on at the mo, but later if you do load some cheers.

Agree on the 250 with the hole in it. My 70 DT had it, but they were gone by
71 on the 250's, I believe. Round swing arm like the 73 has. Wonder if there is
a bulletin about it? Not smart enough to do the offsite photo thing.

CT never had the "knob" steering damper. 

Not likely at all Yamaha would use an older swingarm either.  Sounds to me like someone did some parts swapping in the 53 years since the bike left the factory.

img.doerig.dev
  Dennis just go to this website and upload your image and copy and paste it’s free and you don’t have to register your name etc

I'll try that pic loading idea myself.
i.imgur.com/Y2dgNvO.jpeg
Oh, was expecting a photo not the link--which works anyway just hit link to bring it up. But am i doing it wrong.

Understand on the parts swapping. I wonder what could have happened to a swing arm for it to be replaced though. What could have caused someone to change that steering nut? The bike had two previous owners before me, and I would almost bet the farm that the steering bearings have never been serviced. Just curious about the history. Would like to find an earlier serial number bike to compare. i.imgur.com/xMlH6Vn.jpeg   This is another bike I am working on. Just trying to figure out the picture thing.

RT325, Dennis it works. 

Re photo uploading, go into the image in your Imgur file, then copy and paste the BB code (on the right hand side) to this site and the image(s) will appear AFTER you've completed your post.