Upper control arm ball joint spindles not long enough on disc brake conversion

though I can't remember the taper ratio, offhand, I remember that it is a common ratio, like 3/4" per foot. or 1in per foot.
if you have some dial calipers you can measure the big end diameter(decimal inches) and the small end diameter(decimal inches), & find the difference. Take that difference and divide it by the thickness of the taper hole(in inches) in the knuckle, then equate it to "x""/12", and solve for "x". Once you have that, you can beg, borrow, rent the correct tapered reamer and ream it out SLIGHTLY bigger. It should not take very much to drop the taper in there. You do not want to expose all the threads, probably one or two threads should be below the nut contacting surface/hidden when fully inserted and torqued to spec.