W2 Headache

I have set of w2 heads that I got in an engine deal. They are 4532693 castings, with closed
chambers. Heads have been ported. they are in the machine shop now for new valves, springs
etc. My problem is there only one set of bolt holes on the exhaust side for bolting the headers up. Everything I seen or have read ,everybody talks about two sets of holes. Can you all tell me what heads these are and what headers I need to buy to work on them. thinking of race only build. 410. h beam rods, flat top pistons zero and deck and 600 something cam with rollers.
950 cfm carb . 727 trans and 488 gears. Hoping mid to low 10's. 500 to 550 horses maybe. Will this work? Been out racing for 30+ years.