Moral of the story is you need a conical section on either side of the barloc. Whether it's a ring, a barrel nut, a recoil lug, etc... does not matter. You could use two Nucleus recoil lugs in between a non-barloc savage barrel nut and your receiver if you had enough threads (ridiculous example, just because you can doesn't mean anyone should/would)....
You don't *have* to torque the barrel nut on the savage prefit version before you torque the screw on the barloc, but it obviously does come recommended from ARC. I have done it several times where I will screw the barrel in to headspace, spin the barrel nut to make contact with the barloc, then simply tighten the screw without torquing the barrel nut. Barrel stays on, zero holds, etc... HOWEVER, I have noticed that you can shift POI around by indexing the barrel nut in different positions (i.e. if you torque the nut one time, but not the next, you're likely to have a very different zero). Torquing the barrel nut first may help with this aspect.
As far as I'm aware there are 2 typical variations of the barloc, each with a "Nuclues" variation.
1) "Shouldered" with a tapered ring on either side of the barloc
1a) "Nucleus Shouldered" with a tapered ring on the front and a Nucleus 'barloc lug' on the rear
2) "Barrel nut" with a barrel nut in the front and tapered ring in the rear
2a) "Nucleus barrel nut" with a barrel nut in the front and a Nucleus 'barloc lug' in the rear.
Bear in mind, 1 and 2 can be used on a Nucleus that has a flat "non- barloc" lug, too. Likewise you can modify existing savage barrel nuts with a 30 degree taper to fit the barloc vs. the ARC nut. Theoretically you could surface machine or lathe turn the face of a receiver (Bighorn, M5, etc..) to build in a tapered ring on the face, and that would work, too-- although it would be a pretty permanent modification.