Don't underestimate the 783. It's no custom Defiance action but it shouldn't be counted out for not being a R700. It's basically a Remington built version of a Savage 10. Nutted barrel, 2-piece bolt, yadda yadda. It's going to have all the benefits of those features which is basically it'll be easy to make it a solid shooter as a DIY project. Whatever you want to do with it, it's a decent donor action for. Since it's a magnum bolt face already and belts kinda suck (even if 7RM is possibly my all time fave), you might consider something in an unbelted magnum like the WSM/RSAUM families. Better brass life and you can custom throat the thing to run long for a little extra case capacity. You canswap out the bolt head to a PTG head on a non-magnum face and run basically any other cartridge that's no longer than a .300wm, even set it up as a switch barrel gun.
If you can't find anything to do with it, send it to me and I'll set it up as a 6XC on my spare barrel.