DD
Thats a pretty Martini, good luck on the loads. I'm just starting to work up some smokeless loads for a 577/500 #2. Tried IMR 4198 and standard primers and got hang fires, going now to Winchester WLRs which are supposed to be hotter. If they don't work I'll use magnums. If the 4198 doesn't work I'll try SR 4759, used it years ago in a 45-120 Sharps with good results. Does your Martini have enough drop in the stock to allow you to get your head down low enough to use the sights compfortably? I had one in 577/500 with a stock so straight I couldn't, have never had that problem with anyother rifle, fellow that had it made must not have had any cheek bone to speak of. Ended up trading it for a 375 Rimless that I could shoot. One thought, before you do anything with the rear sight notch see if you can epoxy or soft solder a white or silver bead onto the front sight just covering the apex of the triangle. I've always disliked that style of sight and would change that before doing anything else, hard part is doing it without altering the rifle.
Best.