It is pretty much same here and I normally just do that. But sometimes I'll get lazy and figure that since I'm turning some bars with 1,5 mm lead I'll do the M16*1,5 and buy the four nuts I only, because I'm not convinced if can find the remaining nuts ever after.
I need to get somewhere box of 4/5/6/8 mm dia dowel pins, those I would need often. Yesterday I cut two dowels out of silver steel (that was closer to 4,9 mm than nominal 5,0 mm).
It's the eternal balance to have enough stuff to keep you going and not accumulating all the stuff that might come handy one of these days.
I considered line boring, but these will not fit into my small lathe and my big lathe (old junk revolver missing the capstan assy and tail stock) would need some little additions. Two pieces are 240*80*30 mm, one 25,00 hole in the middle and two 16H7 holes on both sides. All on on the central line. I'll give some more consideration to your text. Buttons....maybe this is the time to make some, so far I have used bearing rings. I think I don't actually need that accurate here, but it might be a good excercise.
I was thinking of drilling them individually way undersize, drill central hole tight for a dowel that will align them all centrally. Stack three critical ones together, dowel pin on the centre should keep them aligned. Mark orientation on each piece. Drill the whole stack a little undersize and then use hand reamer on critical holes (on the sides). Then take that stack apart, use two holes to align the pieces and bore the central hole clearance.
Would this work?
The Boring bar has enclosed cylindrical slide and boring bar moves in a slot milled to boring head. This slot limits the movement and should make a cranked boring bar to it....I rather build or buy different design for another boring head, but that will "some day" project.