You don't use YaBB's original Recent.pl so it's clear that the mod won't install without some small ajustments.
As step 16 is only a spacing error, you can simply correct it in the mod file.
Step 17 has to be ajusted to the following:
<search for>
$messages[$numfound] = ame|$micon|$mattach|$mip|$message|$mns|$tstate";
</search for>
<replace>
$messages[$numfound] = ame|$micon|$mattach|$mip|$message|$mns|$tstate|$lastmoddate|$lastmoduser";
</replace>
And Step 18 has to look like this:
<search for>
($board, $tnum, $c, $tusername, $tname, $msub, $mname, $memail, $mdate, $musername, $micon, $mattach, $mip, $message, $mns, $tstate) = split( /\|/, $messages[$i] );
</search for>
<replace>
($board, $tnum, $c, $tusername, $tname, $msub, $mname, $memail, $mdate, $musername, $micon, $mattach, $mip, $message, $mns, $tstate, $lastmoddate, $lastmoduser) = split( /\|/, $messages[$i] );
</replace>
Please note that I didn't test those changes and there is no guarantee that it will work properly afterwards.