Welcome to the club, John. If you're thinking of ordering a custom Alembic bass, you've come to the right place. There are folks here that simply amaze me with the knowledge they have and are willing to share. I'm relatively new here myself, but am willing to share my experiences. My playing style and concern for neck width seems to echo yours. I'm confident other, more experienced Alembic Club members will also chime in here to assist you.
To my knowledge, Alembic offers 2 stock neck widths: Comfort and Classic taper. I was very lucky in my search for the right guitar for my playing style and small hand size. I purchased a custom signature 5-string bass from Will Gunn Guitars with a custom neck (Will had built for himself, but never used). The bass I purchased is the Nov. 2000, Featured Custom of the Month named, Coco Bolo Fantasy, and you can look on Alembic's website in the custom archive to find photos.
http://www.alembic.com/info/FC_willg.html My bass was exactly what I was looking for and I'm extremely pleased in every respect.
Anyway, if you use nut and 24th fret dimensions (rather than bridge) in your discussions, you will take the scale differences out of the equation. You also can do the math to convert neck width to string spacing. Here's what Alembic's website has for neck widths compared to my Coco Bolo Fantasy:
Comfort: Nut-1.875 24th-2.93
Classic: Nut-2.0 24th-2.5
Mine: Nut-1.75 24th-2.6875
My personal dilema was the Comfort neck was too wide and the Classic too narrow; not for my fretting hand, but for my right hand. The dimensions of my bass are perfect (for me).
The other important consideration is the neck radius. I have no way to measure mine (I don't have a caliper). But, I can tell you what Will Gunn told me about when he ordered the bass. He asked Alembic to make it as thin as they could with a flat-C shape and they did a wonderful job. It resembles a 60's P-bass, slab neck, only with 5 strings instead of 4. The neck on my bass is very stable even though it is quite thin; probably due in part to the 3 ebony laminates.
Finally, after all of this rambling, I suppose it doesn't mean much unless you can put your hands on it. If you're ever in North Dakota, drop me a line and I'd be happy to arrange a time for you to see and play mine.
Dean