I have made triple tree yokes before- and this is the method I use to get it EXACT- I take off the top clamp and draw out the holes that way, so I can measure on a flat piece of ( I actually use cardboard for the first trace) - I have the measurments that way on the cardboard closer than the factory tolerances that they allowed (I have seen more than 1mm difference between Z necks already, my first yokes though were helping my unc do harley mods about 20 years ago, long before cad stuff LOL) - once I get them on card board, I transfer it by tracing again with graph paper, and I get centers and everything from there, to the nth degree. I usually taped this to my raw metal as a template, used machinists die or even paint to make the place like a stencil, and then cut away- never had a single probem that way!
Hope that helps- upper yokes are very easy to make
For the lower yoke, you do the same thing, and the stem hole on the bottom is very exact.
If the machinist is going to do this anyway- I would just take the upper and lower yokes to them- they have everything they need to get the measurments with about 30 minutes max of shop time!
If it takes them longer than that- it is not that good of a machinist!