Two-piece bushings are infact MUCH easier to work with than solid one-piece bushings.
The degree of a one-piece (fixed) bushing cannot be adjusted at all, the only thing you can do is change it's orientation within the beam (which only by sheer luck will result in a correctly aligned frontend that doesn't pull to one side because the caster split can't be set correctly). Only way to know what exact degree bushing is needed beforehand is to throw it on a rack and get some measurements, otherwise you're just guessing.
With 2-piece bushings there's no need to swap back & forth with 0° bushings while on the rack trying to find what exact degree you need... Just reindex it for a different degree and reinsert.
Ingalls, Spicer (AKA Raybestos), Moog, and Specialty Products Inc. all make fully adjustable 2-piece bushings. Of those, the Spicer ones seem a bit above the others in quality.