I have a M1 3 wood with a shaft that I want to put into my new M4 Tour 3 wood.
The M1 have an adjustable adapter and the M4 have not.
Will the shaft be shorter in the M4 head?
The adapter doesn't matter. Pretty sure the M1 fairway has a BBGM of 1.25" - but unfortunately have not measured or seen anyone elses BBGM results with the M4 fairway so can't really say. But I can be pretty sure if there is a difference it likely wont be more than about 1/4". Not really enough to worry about for most.