Are you talking about the 2-piece concentric bushings everyone uses (the only type of "adjustable camber bushing" that I know of)?
I have never had a hard time getting camber and caster in spec on a TTB axle with a solid one-piece adjustable. If one is in and the other is out rotate the bushing 180*. Maybe not both spot on together, but caster has a good bit of tolerance, as long as camber is really good. Those two-piece concentric units give me headaches just trying to read the chart.
I have aligned both my D-28s, my 35, and a number of 44s, along with a few solid 60s and the only one I ever had an issue with had just had the front axle out. I had to have them drive it for two weeks and come back to get the caster set so it didn't pull.
You really don't need to put in a zero bushing and measure it first. On most vehicles with stock suspension you slap in a 0-3 and you will be able to get it in spec.
I will admit that I can't quite hold all the geometry for it in my head, and there may be "technical issues" with what I said, but in my own experience it works. My steering wheel is straight and the edges of my tires are square, and I'm a lazy bastard and haven't rotated my tires in three years.
I did not know the D35's non-adjustable bushings had the hex head though. Seeing as how I was in middle school when that axle was discontinued I'm pretty sure I have never dealt with one in it's factory form, only ones that have been worked on before I got to them. The non-adjustable bushings I am familiar with for the 28, 44 and solid 60 are all round heads.