Sub Articulo 39.2
When defined normally, the baselineskip above a paragraph is the value
for within that paragraph. Thus the baselineskip above headings should
be 17 pt and the baselineskip below should be 14 pt. You want to add
a total of 3*14-(17+14) = 11 pt space. It is up to you how you distribute
it.
Since the text below the title has a smaller baselineskip, you may want
to reduce the \prevdepth parameter after the title to avoid getting
a \lineskip. E.g.,
\vskip-.5\prevdepth \prevdepth=.5\prevdepth
But it will probably not be an issue with 10 and 12pt text.
>2. When a heading is too wide to fit on a single row, I would expect the
>baseline of the second row to be 17pt below the baseline of the first. But
>this isn't so.
Ah! You have your headings defined badly. Somehow your font size
is being forgotten before the paragraph ends. It works properly
when you use \@startsection normally.
>3. I want the first row of text in each chapter to start at exactly the same
>height.
Just specify the size of the box and some fill-glue:
\vbox to 1in{\vfill }
or
\parbox[b][1in][b]{\linewidth}{}
which puts all titles at the same baseline. To put them
at the same top line:
\vbox to 1in{\vfill }
or
\parbox[t][1in][t]{\linewidth}{}