I was recently given a 1975 DT250 by the duaghter of a longtime friend that passed recently.
He had aquired it in a bike trade deal in non operational condition several years ago and it's still that way.
It's only showing 1900 miles on the odometer and still has lots of tread on the dry rotted Dunlop Trials Universal tires and the skid plate looks pretty unscathed so I'm guessing that the mileage "might" be correct but---
 the coil ohms out at 12 ohms unhooked and it looks like there has been water inside the magneto cover. I have the mag rotor puller tool on order to get a better look along with a cheap coil.
The Mikuni carb was pretty clean inside minus some varnish but the lower o-ring that pushes into the float bowl had been pinched when last messed with. I have a carb kit coming for that.
There was the required mouses nest inside the airbox that caused it to rust out but I think it can be saved with a trip through the sand blaster.
Basically, time and less than optimal storage conditions hasn't been to nice to it but it could be much worse.
I plan on hearing it make noise before spending much more on parts---- that seem to be hard to find ---and pricey these days. 
I did own a '73 DT360 in my Navy days in San Diego, 45 years ago and still have the manual for it but this bike did come with a Clymers manual---that I'm not really fond of. 
Well, theres my intro folks. I'll pester you when necessary but holpefully the search engine here runs good.
Ya'll ride safe!!
 

Greetings from Tennessee  

Welcome from NZ. I hope the carb kit has that little Oring otherwise members on here know all the tricks & where to get them from.
12 ohms sounds odd for the coil--even a faulty one-- but primary side-- the single wire in, with meter to the coil framework should be very little coule of ohms but plug lead to earth or through to the 'in' wire should be up in the thousands maybe 5 thou guessing minus plug cap & double that through the cap. Good old DT, give the points a scratch & you might be surprised. What ohms meter are you using. I'm still stuck in analogue meter mode lol & can't handle these digital things.

 from near Salisbury, Wiltshire.

Be sure to change both sets of brake shoes once you get it running - Yamaha should still stock these.

RT325 will have you running by lunch! So many well seasoned folks with these bikes AND the tech library to help along the way…