I don’t think the cocking piece is a great place to put the rear sight. Probably a non-starter if you want a consistent, solidly mounted rear sight so it will actually be an advantage in accuracy. With the Mojo referred to earlier, there is actually a peep out there that is designed for and works on the rifle. That will do to start with.
However, out on the barrel may not be the most advantageous place for a rear peep. US military peeps from the 1903A3 forward through WWII and then the M16s I was issued, and my own iron sighted ARs, have the peep a lot closer to the eye, taking full advantage of whatever sighting length is available on the particular rifle. The original 1903 had the rear leaf out in the barrel, though, but the receiver was amenable to a redesign to a superior sighting system. With the MN, you have milsurp receiver that was never meant for a peep, and isn’t really compatible with putting a rear sight of any description anywhere but on the barrel: the split rear ring, and the vertical bolt handle when turned to cycle the action really don’t allow for mounting on top because there’s nowhere to put it.
The way to really do it would be to mill off some of the left side wood and drill and tap for a side mount peep, but even then, the straight bolt handle going vertical to cycle and the split rear receiver ring are going to dictate placement to such a degree that you may not get much benefit from the project vs just using a Mojo when all is said and done. The sniper version’s scope attachments required quite a bit of modification to the rifle to get it to work: milling the stock and receiver, drilling and tapping for the bent-over the top mount, bending the bolt handle to clear the little scope and mount.
Doing something similar for a peep, like on a Winchester 94, probably won’t get the peep too much further to the rear than the front of the receiver. I doubt trying to cut into the receiver front, where the barrel threads are, to put a peep on it is going to be a wonderful plan. In any case, whether a side mount or D&T into the front of the receiver is only going to get it back a few inches at best from the original rear sight slot, and that won’t give the benefits of mounting it on the rear of the receiver.
I could be wrong. I’d like to see the end product if I am.
ETA: apparently, there are those with more knowledge than I of how to do little things like drill into rifle receivers. This is for a Rock Solid scope mount, but does show that a rear peep on the forward receiver could be possibly be done.