As always I got it working just after I posted this.. here’s the code I used..
<script>
jQuery( document ).ready(function() {
var Trial = jQuery('.gallery-size-thumbnail').find('a:first').attr("href");
jQuery("#open-slider").attr("href", Trial);
var Text = '<a href="' + Trial +'" data-width="1365" data-height="2048" class="eltd-btn eltd-btn-large eltd-btn-outline eltd-btn-line-left"><span class="eltd-btn-text">View Photos</span></a>';
jQuery( ".eltd-page-title.entry-title" ).after( Text );
});
</script>
Hopefully it can be useful for someone else!