Winching is dangerous. Use your best judgement and if it doesn't seem safe to you, don't do it.
That said...
Winch with the trany & transfer in neutral. You don't want any of these forces having any shot at your driveline.
Use the brakes to hold your truck.
If the brakes can't hold your truck, i.e. you're sliding towards the winching direction, change to a double line pull with a remote anchor. I.e. offload half the pull from your truck.
If you are using brakes & a remote anchor and you're still sliding, then consider anchoring your truck.
IMHO to anchor, run straps from your front recovery points under the truck and then back to an anchor instead of using the rear recovery points. Put all of the anchor pull through the winch mounting platform, not your truck.
So, if you're doing an anchored pull you will need from the remote anchor back:
tree saver or pullpall, shackle, cable hook, snatch block, shackle, winch, winch mounting system (ARB, Slee or similar), recovery points, 2 shackles, 2 straps, shackle, anchor run (strap, cable or choke chain), shackle, tree saver or pullpall.
In this scenario with a 12000lb rated winch (~10,000 lb real pull if I understand right) you will be exerting enough pull to lift approximately 4 of our FZJ80s straight up into the air simultaneously.
These forces are insane and dangerous. IMHO the weak link in the above needs to be the winch itself. All anchor shackles should be rated to 6+ tons. The shackle with the snatch block on it should be rated at 12 tons. I have a 15 ton shackle. Its a monster. The thing is so big that it won't fit anything but the ARB block.
Use extreme caution with this kind of high stress rigging. It is the most dangerous thing you're likely to do unless you work in comercial fishing.
