AddField - Align Top And Center Of A Page Regardless Or Orientation?

I need to add a form field to be on the top - centered on the page regardless if the page is portiat or landscape. Is this possible? Everything works like a Charm with the exception of the alignment on the different page orientation - Here is what I have so far:

// add form field to each page of the PDF for (var pageNumber = 0; pageNumber < this.numPages; pageNumber++) { var dateStamp = this.addField("DateStamp","text",pageNumber,[450,770,155,790]); dateStamp.textSize=10; dateStamp.textColor=color.red;} this.setAction("WillPrint", "var today = new Date(); var current_hour = today.getHours(); var current_minute = today.getMinutes(); this.getField('DateStamp').value = "Valid 24 Hours From Printed Date... " + util.printd("dd/mmm/yyyy",new Date()) + " " + current_hour + ":" + current_minute;");