My rig has civvy sourced Crosby 6 1/2 ton screw pin shackles on it. I used to work industrial construction so they were pretty easy to come by used ($25 for a 3 gallon bucket of assorted "retired" rigging at the Ironworker's supply I go to). If they have the slightest bit of damage they can never again be used for critical jobs, so if they're damaged (nicked threads, spread ears, worn out markings) they are no longer kept on the jobsite. You can often get used rigging for free if you are buds with an Ironworker or Crane Operator. If it fails OSHA requirements, it usually gets removed from the jobsite immediately. Companies don't like fines. New they cost something like $60 each, but you don't need new/certified if you're just using them to pull an old truck out of the mud.
Shackles are measured by body diameter, not pin diameter. 7/8" (6 1//2 ton) shackles use a 1" diameter pin, so those are the ones you want to look for. Regular civvy screw pin shackles are more convenient than the MIL style "safety" type ones in my opinion and I use my bumper shackles pretty frequently, so I'm not particularly bothered by that fact they are not restoration correct. Most brands require light grinding with a flap wheel in order to remove the line left by the forging dies on the inside of the ears in order to fit over the CUCV rectangle tubing mounts. Even with light grinding, the weak point is still going to be the mount itself, not the shackle. Just make sure they never wind up being used in certified rigging again if they've been modified or repaired in any way. I put a small grinder mark on the ear to avoid potential confusion and ID them as "mine".
You have to be able to take the shackles off (or keep a few spare shackles handy) in order to hook up a cable or sling eye, so I do not weld the pins on or bend any cotter pins on safety style shackles. I weld for a living so I don't doubt my abilities, but I feel It kinda defeats the whole purpose if you make them non-removable. I always have a large adjustable Spud wrench on the truck, so if somebody wants to steal them they're going to need a similar tool to take them off. So far just tightening them up after use with a wrench after use has been enough to keep the honest folks honest (knock on wood!).