Looks like a 302 to me, the quick way to tell the 302 windsor from the 351 windsor is on the 302 the lower bolt on the thermostat housing is right behind the top of the water pump, on the 351 the same bolt is just above the water pump, about 2 inches higher.
the reason its higher is the 351 has a taller deck height.
the 351 cleveland, which your car (H engine code) originally had has the upper radiator hose going into the block veritically right next to the distributor.
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