Yes the Francotte pattern BSA Martini can be adjusted for Center fire. There is no difference between a centerfire and rim fire in these guns beyond them being adjusted for different striker impact point and load position for the specific cartridge.

I have built a number of them over the years.

The way I was taught at school-American School is not the same as what is laid out in British military Armors manual nor apparently how BSA did it. Several years ago I got a good lecture from a gentleman who supposedly worked for BSA, about how us American's had messed this all up. After the lecture he showed me how to do it right. If he really did work for BSA he would have had to have been 14-15 years old.

He did say the breech block needed bushed for higher pressure cartridges like the .222 Rimmed.

I do not know about the Internationals. I think some have been converted to Hornet. I have just never worked with them.