> INST_GROUPS
>         A list of group names. For each of these groups, some files are
>         installed into a subdirectory of ${PREFIX}.

> INST_FROM.${g}
>         The subdirectory of ${WRKSRC} from where the files are taken.
>         Defaults to ${WRKSRC} itself.

> INST_TO.${g}
>         The subdirectory of ${PREFIX} where the files are installed.
>         No default value.

> INST_FILES.${g}
>         The list of files that are installed. May include globbing
>         patterns.
>         No default value.

This looks very good for me.
But one thing is probably missed: permissions (or the installations program,
INSTALL_DATA, INSTALL_SCRIPT etc.).

-- 
Best regards, Aleksey Cheusov.