Several US makers used the taper choke system. Offhand I don't recall for certain which ones did & which didn't. The one who did that I am most familiar with was Lefever. OF you come across a Lefever with a parallel section at the muzzle then you can lay Big Odds that it has been opened.

Looking at it strictly from a machinist's viewpoint I do not see it as being any trickier to finish the taper choke than the conical/parallel.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra