Even if the engine number is a 1971, if it was rebuilt, the 1972 head is a direct replacement, so you won't know for sure. They are both the same compression (heads). The piston dish varies to give different ratios.

I think the 500xxx numbers are JDM engines. They sold a ton of 'good used japan engines' during the 80s. In that case it is likely to have the closed chamber head.

Remember, the closed chamber head is good for 1 HP over the open chamber in the A12. The difference is not as much as in american engines or in the later A14/A15 engines, but it's still enough to make a difference.