That is a good looking bike! There's a few spots on that bike I'm like to improve on too:
1.) The rear frame section was lopped off and unfinished - I intended to have a cleaner closeout.
2.) The shocks mount in the factory loctation - Great for simplicity, however the shock angle looks more verticle than aestetically pleasing if trying to match with the fork angle (assuming factory pivot location)
3.) Factory swing arm - heavy.
4.) Rear seat/glass is in line with the tank. I prefer a small offset with the rear seat / glass actually a small step below the tank line. Helps break up 'straight' section of the same color

Restarting progress on this...shortly.
I bought a 1940's Sheldon 11" lathe to help with custom parts (wheel adapters, axle spacers, head pipe spigot, etc) and have to bring 220v to the garage now. In the meantime, I updated my race bike with some fresh plastics and unique graphics. 
I'm eyeing the VAPE ignition now as well, but unsure when to pull the trigger on it since my wife started a business (Residential and Commercial Interior Design). Gotta see how racing and parts fits in with this new phase

Edit:  I guess photos don't work yet. This update is terrible without pics :(

In NZ 220-240 is normal to houses in NZ. I'll run a long lead to your place!!.
Or is your 220, 3 phase for you like 400 'i think' is 3 phase here.
sorry, ignore my woffling lol.

The green paint job is hard to beat on those 73' 250's. My buddy had one years ago, too bad the tanks were both dented, and not an intact fender on it. I kick myself now, should have bought it for a couple hundred. It always ran good.
Carb slide stuck one time, that was entertaining..

I was originally going to go with a navy & gold color scheme but I love this green. I have some dents in my tank that are shallow, so I am considering pulling them and having it reshot with factory green.

Funny about the slide. I rode this bike 1 time before tearing it down. I got stranded 4 blocks from my house with a stuck slide. It seems that as it heated up the bolt-on carb flexed and seized the slide. After it cooled it was free again.
So naturally I'm going to a newer carb and boot-mount to avoid any of those wild demons.  What did your buddy do?

 

It was actually the alignment pin.  Slide twisted and it jammed.  I recall doing something crafty.  tapping it in further, and filing it back to shape. 
As for a warped carb, I've heard others mention filing the flange back flat.  So it doesn't tweak, I presume, when it tightens down.  Too thick of o-ring will also get you into trouble.

I've gone away from using the flange style carbs on my 360.  Actual vm34's are a diamond in the rough with the flange, and I've heard of this issue too often.  If I do use one in the future, I think I'll discard the o-ring, and use just a gasket with some case sealer on it.  Hopefully that helps ya if you do re-use carburetor.

Did the T500 front brake fit the yamaha forks okay or was there a bit of modification

I lost spark, again, on my DT2 and am contemplating installing the Vape on that, I love it on my DT400, it's very reliable.  I didn't start both the DT2 and the DT400 for probably 4 months, they DT400 started right up, the DT2 had no spark but ran fine last time I tried

Dirty points?

If you're asking me Alan, I cleaned them then changed to new ones. No luck!