Power steering pump

Is there any way to identify what power steering pump I have? I am in the process of putting a 1968 gto back on the road. Unfortunately the car has had at least 3 motors in it. When I got it, it had a 1971 Pontiac 400 in it, which I have now replaced with one from either late 1975, or 1976, (also a Pontiac 400 engine code 500557). I need to replace the power steering pump, but when I ordered one it did not have the correct number of bolt holes for mounting. Mine has 2, but the replacement had only one. :confused:

If you go to your local NAPA, they will have an illustrated catalog of reman pumps and can tell you what those pumps fit as far as year and model. You may have to research a little farther an your own to determine exact application, NAPAONLINE.COM has very good pictures too.