[AJD] Unstyled B conundrum

[Mike Scholl]

I looking for an answer to a problem that started in 1945 or 1946.
 
Sometime in 1945 or 1946 my 1935 John Deere B was fitted with a modified short-lug coupler Wico X magneto, I'll assume to replace its 'problematic' F-M DRV2B.  As many of you are aware of, aside from the lug length, there is also a difference in the lag angle between short and long lug coupler.  
 
My Wico X has the 6274 short lug coupler, but the lugs have been lengthened nearly 3/8".  I don't know what was done if anything other than the lug lengthening.
 
In the 30+ years that I've had the tractor, it has always run well, but 2 years ago I decided to restore it so my grandson can drive it in parades and things like that.
 
Since the tractor will be compared to others of similar vintage, I decided that I'd try to get as close to the way it was when it left Waterloo as my pocket book would allow.  With that in mind, I bought a F-M DRV2B.  It is a good mag the throws a nice spark when I bench test it.  
 
Here's my problem... When I put it on the tractor I cannot adjust it to where the impulse trips anywhere near "LH IMPULSE".   It's still too cold here in Minnesota to work in an unheated garage and when it warms up I plan to pull the governor case to see if there are register marks on the cam and governor shaft that might show that I am off register.  I've explained my problem to an expert and been told that there is a fair chance that I'm looking in the right direction.
 
Here's my question... Is there anyone out there that has encountered a similar situation that can say "Yes, this was a common practice" or "No, a single gear tooth off would give you more than the difference in lag angle between the long and short lugs".
 
Any insight is appreciated!
 
Thanks in advance,
Mike