the JM guard might be wider than the BAM B40.
I compared my JM Brass guard with a B51 guard and they were very close.
The JM guard fits the TX200 or ProSport.
I don't know if the guard for the B40 is like a B50/51 or if it's more like the TX/PS.
Here's a pic showing the relationship between the two:
Sorry I can't compare directly to a B40 guard, but you might be able to come to a conclusion from this. If your guard looks more like the B50/51 guard, you'll probably have to chisel out a little wood to make it fit. It should definitely look nice on your B40!