<center><img src="http://ic.pics.livejournal.com/sshg_pf_mod/56313174/21678/21678_original.png" alt="Pygmy Puffs (G)" style="max-height: 3475px;" width="600" height="3475" border="0" /></center></lj-cut>
See that bolded style attribute? That's what one must set to the desired height in pixels in order to override LJ's CSS. LJ has a lot of these annoying style-related issues (I thought I knew them all), and I completely missed this one because no one's ever submitted an image this long and Firefox, my default browser, ignores LJ's CSS directive.
Thank goodness the comic is now properly displaying! *\o/*