I have a '14 75B in 40 and a '15 SP01 9mm. I've thought about this so I tested fit of the Sp01 9mm barrel in the slide and on the frame of the 75B.
The SP01 and 40 barrels had the same OD at the muzzle, but that was about it. The .40 SW barrel had larger barrel hood, lugs, and cam. The 9mm sp01 barrel was swimming in the 40 slide and didn't lock up tight at all. Conversely, the .40 barrel did not fit my SP01 slide or frame. The lugs and barrel hood would not seat into the slide. Without the slide, the cam/ramp would not fit the frame.
Reaming the sp01 9mm barrel I have would make for a thin walled chamber and a very loose barrel in the .40 sw 75B.
Anyone have positive experiences with the swap? is it year dependent?
Comparison of my 75B .40 barrel (silver) vs the 9mm SP01 barrel (black):
The lugs and barrel cam are just a tad bit beefier on the .40
I can't make a 40 SP01 to 9 SP01 comparison, the 40 SP01 is still on my wish list...