HI,
I looked at in AutoCad and I see sections where the curve goes negative. These are the wobbles in your plot. In my experience with smaller horns a constant radius will fit to the expansion within tolerances anyone is likely to hold during construction. I don't know if that holds true for these big boys but measuring a curve from the outside of the horn should be easier. All you need is a straight board with a center mark and a ruler.

BTW, if you need them I can make printable templates and email them to you but we will need to get the curve plotted accurately first.