Disclaimer / Notice: This was done because my post was not answered and I needed a solution. If there are problems in the code, please do step in and point them out. I am not a coder. I have no idea if this is inefficient or causes undue strain on the server/database. 
Please use at your own risk and be sure to back up any files (db, template, system, etc.) before modifying them.
System New Members block mod/clone -
In modules/system/blocks/system_blocks.php, add this code after the b_system_topposters_edit block of code (not sure if it matters where it's placed):
 function b_system_yourvariable_show($options) 
{ 
    $block = array(); 
    $criteria = new CriteriaCompo(new Criteria('level', 0, '>')); 
$criteria->add(new Criteria('fieldname', 1));     
$limit = (!empty($options[0])) ? $options[0] : 10; 
     $criteria->setOrder('ASC'); 
 $criteria->setSort('uname'); 
    $criteria->setLimit($limit); 
$profile_handler =& xoops_gethandler('profile'); 
$fields =& $profile_handler->loadFields(); 
    $member_handler =& xoops_gethandler('member'); 
    $yourvariable =& $member_handler->getUsers($criteria); 
    $count = count($yourvariable); 
  for ($i = 0; $i < $count; $i++) { 
        if ($options[1] == 1 ) { 
            $block['users'][$i]['avatar'] = $yourvariable[$i]->getVar('user_avatar') != 'blank.gif' ? XOOPS_UPLOAD_URL.'/'.$yourvariable[$i]->getVar('user_avatar') : ''; 
        } else { 
            $block['users'][$i]['avatar'] = ''; 
        } 
        $block['users'][$i]['id'] = $yourvariable[$i]->getVar('uid'); 
        $block['users'][$i]['name'] = $yourvariable[$i]->getVar('uname'); 
  $block['users'][$i]['field_title'] = $yourvariable[$i]->getVar('field_name'); 
   $block['users'][$i]['field_title2'] = $yourvariable[$i]->getVar('field_name2'); 
    } 
    return $block; 
}  
Replace all instances of "yourvariable" with your own title. Replace all instances of field_name field_title with the name/title of your custom field(s) used in extended profiles module. Along with other criteria, it pulls users meeting this:
$criteria->add(new Criteria('fieldname', 1)); 
Which is a yes/no radio button I set as a custom field. 
After function b_system_newmembers_edit($options) code block add:
 function b_system_yourvariable_edit($options) 
{ 
    $inputtag = ".$options[0]."' />"; 
    $form = sprintf(_MB_SYSTEM_DISPLAY,$inputtag); 
    $form .= "
"._MB_SYSTEM_DISPLAYA." ; 
    if ( $options[1] == 1 ) { 
        $form .= " checked='checked'"; 
    } 
    $form .= " /> "._YES."; 
    if ( $options[1] == 0 ) { 
        $form .= " checked='checked'"; 
    } 
    $form .= " /> "._NO.""; 
    return $form; 
}  
Next in - system/xoops_version.php above the comment // Profile fields - add:
 // Your_title Block 
$modversion['blocks'][14]['file'] = "system_blocks.php"; 
$modversion['blocks'][14]['name'] = _MI_SYSTEM_BNAME15; 
$modversion['blocks'][14]['description'] = "Your Description"; 
$modversion['blocks'][14]['show_func'] = "b_system_yourvariable_show"; 
$modversion['blocks'][14]['options'] = "10|1"; 
$modversion['blocks'][14]['edit_func'] = "b_system_yourvariable_edit"; 
$modversion['blocks'][14]['template'] = 'system_block_yourvariable.html';  
Make sure the _MI_SYSTEM_BNAME is the correct # for your system then modify the system/language/english/modinfo.php file to incorporate _MI_SYSTEM_BNAME#.
Add the system_block_yourvariable.html to modules/system/templates/blocks/ directory. If I remember correctly, I copied system_block_newusers.html and modified it to suit my needs - using <{$user.field_title}> in the template.
Update the system module.
You should now be able to add and set the parameters of the new block in your blocks admin. 
Good luck!