Gert, check the sight height you need: the sights on the MS are quite low, and if your rear sight is higher than the original leaf, you'll need a taller front sight.

You can't go very high at the front without replacing the ramp, and a tall ramp does not look nice.

How do you want to use the peep? The original tang peep on the MS is only used to put the rear leaf and front blade in focus. If you want to use the aperture as rear sight, you have to remove the rear leaf from the barrel.

On my other rifles I use aperture sights, no leafs on barrel, and fiber optic fronts (CZ rifles, ERA/Recknagel peep sights). I've got a couple of MS rifles at hand and will check the heights available. I also have a cocking piece that has been butchered by a quack smith, and that I can use to experiment.

My own 1903 will arrive in a few weeks, by then I hope to have the peep sight layout ready so I can install it immediately.