Jason Heeris's script worked for me after I changed it to 9999-serial_console (to run later). it only needs to run after 0170-sysvinit, so a lower priority like 1190 would be fine.
a partial fix might be to re-write the offending sed in 0170-sysvinit (UNTESTED):
\(tty[0-9]*\) -> \(tty[A-Z0-9]*\) this would correctly mangle many custom /etc/inittab files.