Thanks for the input, everyone! I see there's not quite one-true-way. This was part of my confusion when I tried searches and looking at existing packages. It helps to know that OCamlMakefile or ocamlbuild use ocamlfind, but hide this detail. From my perspective when this is hidden it just looks like there are even more packaging mechanisms.
I can understand Daniel's tact: choose one sensible method. This helps to force an evolution rather than building up cruft. Certainly making a META file along with descr/opam/url is somewhat redundant. Isn't it?
For now though, I'll do my install steps with ocamlfind using a META file.
It wasn't clear to me that ocamlfind is appropriate for installation, or even how you would use it. Searching, I mostly get matches for using ocamlfind to install existing packages, not make something installable. The "install" subsection of ocamlfind really gives the impression of an end-user tool, not for a library creator. References are made to the META file but no description of this file.
Searching for the META file related to OCaml doesn't fare too well either. Then I realized "man META" actually gives me exactly what I was looking for. I didn't expect that, since I'd expect other systems could have a configuration file called META.
Anyway, thanks! If there isn't an explanation of packaging libraries somewhere, maybe I'll make a blog post: "How to share your library". It's the kind of thing which might seem like nothing once you know it.
-Tony