For what it is worth, I have found that unless you are a competition shooter, most factory barrels are more accurate than we can hold.
A&B barrels are more so, and on up to those really expensive ones. Unless the get screwed on to the action incorrectly, they will all shoot.
The rest is just window dressing so if you like a fiberglass stock (and can find an appropriate one) go for it.
The same with cartridges. As long as it fits the bolt head and it is what you want, it will work. You mentioned 260 Remington, I don't know if it is the same head size as the 7.65x53 but if it is, great.
I used to prefer the 6.5x55 Swedish cartridge and would argue it as a better choice. Now I prefer larger caliber.
Have you considered using the 7.65x53 as the basis for a wildcat? Maybe 35 or 40 caliber?
Bottom line is custom rifles are what you want them to be. Everyone will make suggestions but you have to wade through it all to choose.
Look at the options.
For what you can spend on a custom, you could buy several off the shelf models.