Lots of optics options shown on the refinishing a Cooey sticky on this page - I posted this there and may help you if you decide to go with a red dot. I would suggest a Bushnell TRS25 rather than what I mounted on this Model 39:
Something that may help folks out in a similar situation.
A friend wanted a single shot 22 for his son for Christmas. I managed to find him a Cooey 39 in nice shape from a buddy at the gun club who had redone the stock when he got it for his kids years ago. Bluing is a bit thin but not bad.
My friend wanted a red dot on it for his son to learn how to shoot, As you know the receiver area is pretty small to do that with (although lots of pics of others that have done so). I mocked up something else and with his ok went through with it. The rear sight is attached by a screw into a drilled and tapped filler plate in the dovetail. The screw has to bottom out on the dovetail to hold it in place.
I determined that a 10-32 screw would fit the filler plate hole. I picked up a package from CTC and then using a file and drill, reshaped the head to fit a Weaver 76 single hole base mount and cut to proper length with a dremel cut off. It has a 8-40 screw so I had to ream the hole out with a #11 drill bit. A dab of cold blue on the screw (although it doesnt look like it in the picture).
The base sits slightly above the barrel, so I roughed up the bottom of the base slightly, and put some JB weld on it and then screwed it into the filler plate so that it would bond to the barrel. Lined up the base and the barrel and let it set up. I wanted to make sure that for a young person he wouldnt knock the base loose. Waited 24 hours, all solid, removed the screw and put some blue lock tight on it and snugged it up..
Put a TruGlo red dot on it (a TRS25 would be sleeker) and its ready to go. Leaves the bolt area open so can see if cocked or not.
Its on straight, just the camera angle
