On my GMCs I use some really cool looking nuts and washers from McMaster-Carr. I use a stud in head threaded hole first with part showing fine thread.
I buy Bellville washers which keep pressure on the manifolds and then use flanged nuts either 6 or 12 point. The Bellvilles are usually larger in diameter and work will the the manifold clips. I used smaller diameter Bellvilles by buying 5/16" and filling the holes if needed in the tight spots. The 12 point flanged nuts look the best.....Good luck
