Samco snipers were "real" snipers that were used by the Russians during WWII. After the war they were sent to Yugoslavia for use there. The optics were removed when they were no longer being used for other systems. The rifles were sold in their "original sniper configuration. They were not reworked and put into standard M91/30 service. They are snipers and have always have been snipers.
Replacing the optics and mount and base is generally OK because everyone knows that the Yugo's lost their optics so you are not trying to fool anyone. It is commonly known.
Replacing the optics and mount and base like they do when they "resniper" an "ex-sniper" that was 91/30 standard service is a deliberate attempt at forgery or commonly known as a "fake".
So in general, re-scoping Yugo's is allowed.
Personally, I'd rather own a Yugo that has been re-scoped then some of the other "questionable" sniper rifles that have been accepted and imported to the USA. But that is just me.
As for the base fitting to the receiver. There are generally no two sniper bases exactly the same. That is because the Russians did not use templates to drill and tap their snipers in WWII (PU Snipers that is). So the pin dimensions can vary in distance to one another and also in location. This is a big problem as your chances of getting a base that will fit your pins and tapped holes in the receiver is slim to none. On mine, all the tapped holes matched (thank God)
and one pin. The second pin was off by less then a 1/6 of an inch. I removed the original pin and stored it away. I use a reproduction pin and took just a little off the side of it so it would fit into the base pin hole. I was very lucky. I have known guy that trade the bases off till they find one that will work. That could take over 20 trades to find.
But the re-scoping of the rifle is not why people collect these rifles. Shooting them is not why they collect them either. They collect them because they are unique and hard to find.
For example. I have two Romanian Mauser snipers used in WWII. Both are missing scopes. One has a scope mount. Both have the base. I collect them because they are rare and unique. Not to fire them. They lost their optics the same way after WWII. The scopes are so hard to find, that I have only seen one for sale in the last 12 years. So people put in what are called "filler scope". Everyone knows that is not the original scope, but it's OK because no one is trying to screw anyone over. It is not considered a "fake". Just a sniper with a filler scope. Also, they say they are a filler scope when they present them. Me, I left mine the way they came to me. I have other Mausers with scopes on them if I want to go shooting.
Same thing for these Yugo snipers. It has been acceptable to re-scope then because the rifle has
ALWAYS been in "sniper configuration", and still is.
Darryl