In general, and for all practical purposes, 1903 and 1908 model Ms are identical in terms of exterior dimensions. A 1908 model N is significantly different. But a 1905-1906 Browning .25 will fit a model N holster. They are virtually the same pistol, but not 100% identical.
Some 1903s can be swapped out to run .380 acp, but it is not true for all of 'em. Some .32 frames have suffucient clearance to allow seating of a slightly wider .380 magazine, but not all.
I have tried some of mine and, sure enough, some will do it and others won't.
A .380 barrel will swap out easy and for sure in a type III.
Now y'all got be perplexed and wonderin' if type II barrels will swap out the same.
I'm gonna go check it out this afternoon, but I suspect they will.
Q: Will a type II 1908 model M swap magazine and barrel with a 1903 type II and be runnable, and vice versa?
We shall see.......
Keeping in mind: this is a purely pointless question, to the extent that, if folks want a .380, then buy a .380, and same for a .32.
Edit: I cannot find the combination of magazines, frames & barrels that I used to swap out. I did it once, and I must have gotten lucky, because I can't find the ones that worked now. Just goes to show ya.........