As you can see by this chart from Damper Doctor, 350 dampers were offered in 12:00 O'Clock, 2:00 O'Clock and 2:30 O'Clock configurations. You must use the correct front cover to match or change the timing tab on your cover if you definitely know you have found TDC. If you haven't found absolute TDC, let us know and we'll outline the procedure.
http://www.damperdoctor.com/Merchant...egory_Code=CHE