GPJ, I fully agree with the "no scope on this rifle" part, and I've been through the same questions regarding a peep - ending up at the same point: the best place to do that is on the top of the bolt sleeve/cocking piece. It's relatively easy to find a spare one to experiment and to use for that, keeping the original for later use if needed.

Now, that top is bored, but after 9-10mm the hole reduces in diameter, and there is actually enough "meat" to dovetail the top, or even to drill straight through for an aperture sight - approximately 2.5mm at maximum thickness.

If you drill for the peep, you won't have much room for vertical adjustment, and you'll need a very fine thread (0.5mm max, which gives you 0.25 mm adjustment for a half turn, which translates in 40-50mm of change at 100m, depending on your sight radius.

If you dovetail, you'll have more options.

Whatever you do, please keep us posted, I'm really keen to see the outcome because I'll soon have to do the same...