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One neck attachment scheme. The barrel bolts are 3/8" rod, length to suit, tapped 10-24, with a fat washer under the heads (inexplicably not shown). An appropriate neck block with a squeak-ish fit helps things along - any centerline alignment issues are ready for solving.
It's a hell-for-stout approach. I made a long L-wrench for tightening from an Allen wrench, some tubing, Loctite, and stainless (!) rod from a political yard sign; access through an end peg hole. You can figure it out. (I got more goodness out of that yard sign than I did out of the politician, by the way.)