The primary advantage to shooting 7.62x54R is because the surplus ammo is dirt cheap. If accuracy is you goal, that reason is gone.
The surplus ammo is awful. The bullets are sized wrong for most of the barrels. Ballistically speaking, it's nearly the same as aught six, and God knows there are plenty of accurate versions of those out and about. As I mentioned, I have limited space and storage, so if I could keep my hunting and target guns the same, I'd be pleased.
If you are already set up to reload for the 54R, all you need is dies. For a custom bolt gun, you are going to want to neck size anyway. A set of Lee Collet dies is what, $30? You are going to spend 5 times that modifying your bolt and getting an oddball barrel.
I neck size anywho... I use a Lee handloader (whack-a-mole). I like the cartridge, and would like to continue working with it. I am a big believer in consolidating cartridges to reduce my inventory on hand. From that link HKfan posted earlier, it looks like I can use a stocker Mosin bolt and a very, very cheap barrel that should perform nicely.
If that is you goal, why not go for something even more obscure, like 9.5x57mm Mannlicher-Schönauer. Maybe you could do an Ackley improved version. It would really be unlike anyone else's range toy in the world
I have no experience or equipment relating to those rounds. While I'm sure it would be unique, I am looking for a combination of price, uniqueness, compatibility with my current equipment and whims - much like anyone else who has spec'd a gun. I appreciate that there are different paths to take to get to the goal I envision, but I am looking for constructive advice. I know there is a lot of knowledge on this board, and I've learned a bunch in my five or six years here. However, on this topic, I think I know best what I want, and I'm just looking for some advice on how to make my chosen path there less bumpy.