If using Miata spindles, this is probably the closest thing available to an 'easy button':
http://www.kineticvehicles.com/ControlArms.htmlI believe the Miata has a relatively common 7* taper angle, but has a smaller diameter (and length?) used for the tapered section than the circle track stuff. The wall thickness vs difference in ball joint tapered shaft diameters needs to be taken into account before reaming it out as well, since the more the spindle needs to be reamed out with a taper reamer, the thinner the load bearing walls around the ball joint shaft will get.