[Brian]

Agree with all the above responses; as a machinist, I can tell you that machining a taper is very difficult.
Thing is once you've matched up perfectly the exact taper, next thing is to position it perfectly.
I am away from my logarithm tables at present, but if you calculate the sine/cosine/tangent numbers of the particular included angle of a Ford axle, you'll notice that for every, say one thousanth of an inch you remove from the taper, the longitudinal distance the mating taper will travel along said taper is , I dunno, maybe 12 thou?
Recently I rebuilt my diff using all NOS/NORS parts. I used NORS axles. One axle has the taper machined too small; it requires a shim in order to position the brakedrum in such a position it doesn't bottom out on backing plate.
Trust me, it'll be easier to locate correct axles for your application than attempt to shorten up longer axles.