Find a 3/4 6pt deepwell socket, I suggest the impact version. (no hard chrome plating to drill through)

Drill a #41

Photos:
You can use pliers to pull it loose when done. Use caution; if you cannot see threads in the barrel nut spanner hole it's probably over the key slot. DON"T push your pin in too deep, it'll lock in the key slot. And it's still a deep well Socket


Now if I can just figure a way to make the spanner for the jacket w/o a lathe or mill....