Search in Postbit_legacy for the following.
1) To make the Username Central.
Find:
<div id="postmenu_$post[postid]">
Replace With:
<div id="postmenu_$post[postid]" align="center">
2) To make the Usertitle Central.
Find:
<if condition="$post['usertitle']"><div class="smallfont">$post[usertitle]</div></if>
Replace with:
<if condition="$post['usertitle']"><div class="smallfont" align="center">$post[usertitle]</div></if>
3) To make the Rank Central.
Find:
<if condition="$post['rank']"><div class="smallfont">$post[rank]</div></if>
Replace With:
<if condition="$post['rank']"><br /><div class="smallfont" align="center">$post[rank]</div></if>
4) To make the Avatar Central.
Find:
<if condition="$show['avatar']">
<div class="smallfont">
<br /><a href="member.php?$session[sessionurl]u=$post[userid]"><img src="$post[avatarurl]" $post[avwidth] $post[avheight] alt="<phrase 1="$post[username]">$vbphrase[xs_avatar]</phrase>" border="0" /></a>
</div>
</if>
Replace With:
<if condition="$show['avatar']">
<div class="smallfont" align="center">
<br /><a href="member.php?$session[sessionurl]u=$post[userid]"><img src="$post[avatarurl]" $post[avwidth] $post[avheight] alt="<phrase 1="$post[username]">$vbphrase[xs_avatar]</phrase>" border="0" /></a>
</div>
</if>
