Spluttered & backfired through the exhaust sounds just like its broken the flywheel crank key--same symptoms. But if you don't have spark then that's ruled out. So definitely 'No Spark' when you spin it.? sorry, had to ask didn't i.
Will still spark with key destroyed--just spark in the wrong place, hence backfire out the pipe.

might check and see if the flywheel loosened up and it shearing the key. if the points check out by Mark T's method, I would look at the possibility of a sheared flywheel key.

Zero spark, key in great shape - pulled the flywheel off to stare at stator hoping it would something obvious would jump out at me

Thanks for the reply, key is in perfect condition..

Oh, damn, but in one way its good its not broken. But nothing jumped out i guess. Now its super important to tighten it very tight so it doesn't break the key. But back to why no spark--what can i say. If points are clean & contacting & all wires joining somewhere from points-source & condenser before exiting to the loom & top coil & without shorting somewhere--i'm out of ideas. Make it battery ignition that'll fix it. Good luck.

Maybe I missed something, but as MarkT said, you must see 0 ohms with the points closed or you will never get spark. That is where you need to focus. Sanding the points can help smooth the surface, but often leaves debris behind. You must follow up with the "strips of white card" process described. Also, if you have some contact cleaner, spray that first, then use the white strips. If you still don't get zero ohms resistance with the points closed, track down the points wire to condenser/source coil termination. (the points simply short the source to ground when they are closed) 
Another thought, you are verifying the zero on your meter by shorting the test leads, correct?

I have not been able to clean the points as of yet but will as soon as I'm able.  I do have electrical contact cleaner and will use that to clean prior to the business card cleaning as described.  As for verifying zero on my meter I'm not sure what you mean, as previously stated electrical is a black art to me.  I am testing the black wire coming from the stator, disconnected from the rest of the system if that's what you mean...  I do appreciate your thoughts and suggestions!

Just using contact cleaner on the points isn't going to help, I actually removed mine and cut long strips of 1000 grit sandpaper. Then I pulled those strips through the points many times, alternating between the top contact and the bottom contact. Only one screw holds in the points, and they're very easy to remove. Just remove the one wire that's connected to them. Mine were pitted and corroded, and I got them polished mirror smooth now. By the way the wire connected to my points was only hand tight. It can be a little tricky to tighten that up if you don't have those tiny ignition wrenches.

Also, is your high-tension lead from the coil to the spark plug in good shape? If not, I picked up some 7 mm high-tension lead at O'Reilly Auto Parts. They sell it for $1.09 per foot. I'm assuming you have the kind of spark plug connection where the ends come off, and are not molded on. Also take a look inside the coil and spark plug connectors, make sure there's no corrosion in there.

MarkT.
I'm using an old [faithful] analogue meter that seems to stop at 1 as run out of needle adjustment. So i have trouble getting my head around a zero reading [Mark put me right please as don't want to put people wrong], but isn't the source & condenser still giving a reading as wires are connected to the points? Yes/No--or put me back in the bad boy corner. If you saw the points on my old DT1--well fizzed most likely from probably 30 years of minimal running but never fails. Do you mean say with a digital meter it defo should zero out to 00. Sorry & thanks.

Ok so rethinking my post, with points closed is it a total short to earth 00 no mater what's connected to the points?. Think i answered my own question haha.

Was googling trying to find a pic of a genuine vintage points checker meter like i had in the "60's & then left the batteries in for the next 50 years & ruined it bugger it. Anyway--couldn't find one. It was an anologue meter with i suppose very very low resistance? with adjustable needle knob thingy & worked great. Well if only i knew i'd need it 50 yers later with back to the future points ignition like we're now playing with 'again'. But in my googling i found this youtube of BigDog from 2015. Good to see.