I recently acquired a pair of bikes one is I believe  a 74 mx125a, the other is an 80 that I haven't looked at too close yet. I have a question about the stator/ source coil assembly on the 125. I removed the flywheel to inspect the points etc.. to attempt to get this thing running and found that everything behind the flywheel had been ripped from the mounting plate and mangled beyond recognition. The information I have found shows a set of points a condenser a source coil and a source coil core with no windings on it. My question is this, is that steel core with no windings required? I can't find a part number for one, and the factory parts catalog shows it included with the base/plate. None of the mangled bits I have are salvageable and the baseplate I have found on eBay don't include the coil core. 
  

Yes, some off road magnetos came with a blank iron core instead of a lighting coil. 

Your description of everything ripped loose sounds like maybe somebody tried to use a jaw puller to remove flywheel which can also damage flywheel...  any other cause would almost certainly destroy the flywheel. Would be interesting to see pictures of the carnage.

At this point you might be better off finding a complete ignition from a DT or MX. 

Here are some pictures of the carnage, flywheel is toast also. This bike is fresh from the weeds but mostly complete

Ouch.  Something came loose under there when the engine was running.  What a mess. 

Stator OD should be 120mm...  complete ignition system from a 74-76 DT175, 78-81 DT125/DT175, or 77-79 IT175 would all work or various MX/YZ 125 ignitions from 1974 on....  obviously if you pick a CDI model you need the CDI box too.

Text is doubling because of a glitch with the "insert all" button.  If you use the "insert" button next to each picture it won't double the text.

Use buttons by pictures to insert photos to avoid doubling text

 




.

Thanks for the list of possible donor bikes for a new ignition system, and the tips on posting pictures.

Man that thing had to be screaming when it let loose.
I couldn't help but save those photos for when you go
"oh yeah, that's nothing. Check this out".

Is it correct that the flywheel is bolted together with basic nylon stop nuts like you see with the two remaining bolts?
 
 

No, would have been riveted.  Someone bolted it afterwards.

But there are three chewed up stop nuts in the photo of the wreckage. And one nut that is still in place shows rotational damage. I am wondering if someone tried running the flywheel with bolts instead of rivets.

Maybe someone actually drilled out the rivets to remove the flywheel, and then they tried bolting it back together after they learned of their mistake. There's a story behind this one I'm sure.