Thank you so much for your help and patience! Got it working with the following:
global $modx;
require_once '/home/project/public_html/config.core.php';
require_once MODX_CORE_PATH.'model/modx/modx.class.php';
$modx = new modX();
$modx->initialize('web');
$modx->getService('error','error.modError');
$siteStartId = $modx->getOption('site_start');
$modx->resource = $modx->getObject('modResource',$modx->getOption('site_start'));
$modx->user = $modx->getObject('modUser',1);
$html = $modx->getChunk('Dropdown');
$html .= "<div id=\"navigation-holder\">
<div class=\"navigation\">
";
$html .= $modx->runSnippet('Wayfinder', array('id' => $modx->getOption('site_start'), 'startId'=>'0', 'level'=>'2','parentRowTpl'=>'ParentRow','lastClass'=>'last','firstClass'=>'first','excludeDocs'=>'34'));
$html .= "</div></div>";
$psheader = $html;
$psnavigation = $psheader;
$coreReplacements['PSNAVIGATION'] = $psnavigation;