Didn't take much of a search to find this. Looks like it came on some L's and LA's.
Edison Splitdorf model RM2 spec. 03757 John Deere part # AL2227T
application L 621,079-624,999
Note: Part # AL2227T was a magneto assembly less a drive gear & impulse drive lug assembly. The above listed tractors used an AL2228T drive gear & impulse drive lug assembly which produced a 10 degrees lag angle. L 625,000-639,999 LA 1,000-4,532 Note: Part # AL2227T was a magneto assembly less a drive gear & impulse drive lug assembly. The above listed tractors used an AL2337T drive gear & impulse drive lug assembly which produced a 20 degrees lag angle. Note: Edison Splitdorf changed the spec.# from 03757 to 03761 during their production of this magneto. We found no information listed in any Edison Splitdorf publications as to why the spec. # changed. We also did not find any information in any John Deere parts book that mentions this spec. # change. Edison Splitdorf was very lax in dating various information. We did find an Edison Splitdorf general magneto application chart that was stamped with a receiving date of January 28th 1943 by the firm it was sent to that mentions that spec. 03757 had been replaced by spec. 03761. We do feel that the spec. # changed prior to 1943. Note: Other than portions of the name plates, which were painted semi-gloss black, the rest of the magneto was not painted.
Here's the site I found the info on.