Hi Paul,
Maybe this script can help, transfer it to a data label after populating the radio button list
<script type="text/javascript">
var count = $(".stack-container label").length;
$("[name='dlCount']").SFCLabel('option', 'text', count);
</script>
Check 'Literal' property for the data label
Add another data label to set the count value, in my script I am setting the value to data label called dlCount.
You can also write stored procedure to return the count if your data source is SQL.
If you have more than one radio button list control on your form/view, the above script will not return the correct count
you can use this for specific Radio button list control:
var count = $( "div[id$='MultiSelectPanel']").eq(0).find('label').length;
** eq(0) is used to select element at index n.
hope that helps