i had a mosin that someone drilled and taped the receiver, it looked like crap and it didnt do much for the value of the gun when i traded it in. as a matter of fact it is still sitting at the gun shop.
i know a somebody makes a bolt on mounting kit i think it might have been on cheaper than dirt. but they look alot nicer. If you get shotgun news i know there are some places that have the sniper kit, but then your talkin $$$$$$. to me the worst thing you can do to a collectable gun is put stuff on it half azzed. hope i was able to help out a little.
+1 for the Darrell scout-mount. A fella I know put one on his M39 Finn M/N and it has been solid. I've tried the "no-name" cheaper brands on my M44, and they sucked. I finally Acra-glassed one to the rear sight block, and that got it to hold. (I did some foolish things to surplus guns in my younger years that I regret now...)
I have heard good about S&K, made here in PA. They make a scout-mount style that has a weaver rail, or uses their proprietary ring system; you choose.
My one pet-peeve with the scout mounts out there is that the scope is set quite high on some, and I think a higher comb to the stock would help. The Darrel mount seems lowest to me.
FWIW, the scout scope marketplace has some really cheap models, then jumps to the Burris/Leupy fodder at $250 +. As it is, I scoped my M/N44 with an NcStar 2.5x, and it has worked quite well. Cost was about $50.00
Typical 5-shot 100yd. groups from my setup result in an average of 2.75" with WOLF 200grain SPs. Not great, but good enough to take a few deer with.
The top pic is a S&K scout mount , made in Pa. Rock solid , if not a little $$$ for the mosin.
The 2nd pic is an ATI mount kit ,"tip" use a drill press not a hand drill , never a problem with it either.
I wouldn't give you a nickel for the B-square mount.
The ATI mount makes it hard to use the safety , these are old pics , but at a later date I welded a ring onto the back of the safety knob "not shown in this pic" making it much more useable.