Well, $out is getting set by:

        for my $col (0..($BUFSIZE-1)) {
            $out[$newrow] |= (1 << $col)
                 if ($in[7 - $col] >> $row & 1);
        }
        $newrow++;
[download]

This is setting the actual bit in $out[$newrow] if the corresponding bit from the transposition source matrix is set.

At any rate, BrowserUk's solution appears to be ideal and small, and exactly fits the requirements; the lack of thorough awareness of the vec() function made this difficult at best. In addition, it makes possible arbitrary matrix sizes, which solved another challenge I had thought of but didn't mention in the original post.

Thanks,
Jason