Mauser 1910 safety catch woes

[Olle]

I just bought a .25 cal Mauser 1910 to use as a parts pistol, but as many of the hard-to-get parts were already gone I decided to use it as a test mule to make my own parts. Seems like the safety catch spring is a pretty elusive part, so right now I'm trying to figure out how to produce this in a fairly rational way. Once I had a few prototypes made, I realized that the frames on my two 1910s are slightly different and the prototypes would only fit one of them. It's just a matter of how the spring is bent so it's no big deal, but it made me curious about some other differences I found.

If you look at the pictures of the test mule, serial #255379, you'll find these features:

-The seat for the safety bar spring is a milled, curved slot
-The grip strap is straight

Also note the shapes of the milled details on the side of the grip.

On my other 1910, serial #244193, you'll find these features:

-The seat for the safety bar is just a milled recess.
-The thickness of the grip strap varies (the grips are, of course, made to fit this)

If you compare with the "test mule", you'll see that the milled details on the side of the grip are quite different.

I guess these are just two subvariations, but I find it rather odd that they changed the seat for the safety catch spring just enough to cause an interchange problem. I don't know if there is much interest or knowledge in the variations of this pistol, but I was hoping that somebody could shed some light on what I'm looking at here.