1.8.5.7 is apparently the current release on the stable, non-multithreaded (1.X) branch: http://sourceforge.net/apps/phpbb/assp/viewforum.php?f=13 Thanks! :)
Hmm, upstream seems to be pretty confused about where to put files in the release tarball. I'm not yet sure how to handle that ...
+ 28 Jul 2011; Patrick Lauer <patrick@gentoo.org> +assp-1.8.5.9.ebuild: + Bump for #363973 +