I have a Garrett HD waste gate actuator that may work for you...it's a used one, bench tested - diaphragm is fine, does not leak down. rod begins to move at about 18#. got it from Kirban's during an Open House - was supposed to be a stock unit (8#) but learned during bench testing it was actually the HD version. I can post a pic later if interested. LMK - I'm not sure if the stock mounting bracket for this actuator with work on a 67's cover.
Garrett part # 1011-144
numbers on label are:
1011-144
03038
50903