IIRC, one idea of the Scout was that ammo would be easily available and powerful enough to do drop game up to about 400 KG (about 880ish pounds) as far away as the shooter could reasonably shoot.
In the US and many other countries, and probably worldwide, the .308 would be the ideal choice. In some countries it's illegal or unobtainable so you'd need to use a different round like maybe 7mm-08 or whatever round is most common (303 British in some maybe?)
But the 7.62x54R?
It's only common in the US because of all the surplus rifles and ammo flooding the market right now. In a few years it will be like the other surplus calibers like the .303 British and 6.5 Swede - available but not exactly cheap. Not really rare but not exactly as common as a rock either. Fortunately, I don't see it following the 7.7Jap or 6.5 Carcano just because there are a lot of Mosins around. But consider the .303 British - the British exercised a lot of influence worldwide at one time but only 60 years or so later, good .303 surplus is nonexistant and the lowest "sporting" ammo you'll find goes for about $11 a box plus shipping.
IMO, I think you'd be better off to go with a .30-30 instead of a Mosin. You lose a little range but realisitcally, you are using a 2x scope - not my idea of a "long range" rifle.
The idea is to hit as far away as you are confident you can hit. With me, I wouldn't lose any range at all with a 30-30 because I am a 250 yard shooter and when I hunt I'd rather be closer than that. I consider myself close enough to a deer when I can feel the heat from it's breath. Anything farther than that is a long shot (hunting is about getting close and being sure, not "sniping").
If you factor in leverevolution ammo the advantage of the '54R starts to get a little fuzzier.
In exchange for that, you get a caliber that is available at any gunshop in several flavors and that is available at walmart for $10/box of decent hunting stuff. And if you had to use it for defense would you rather have quick handling a lever action that you can top off as you shoot or a Mosin Nagant?
Loaded chamber with the safety on - which one gets a shot off quicker?
Mosins are not terribly fast and they are slow to reload without stripper clips and good stripper clips are not that easy to come by.
IMO, a 30-30 fits the Scout concept better than an altered Mosin.
No offense though guys, your Mosins are still very useable rifles at a great price.
And I bet if you went to Finland you would find a whole lot more '54R for sale than you would 30-30.