Not so much by the numbers but by thickness (assuming it has not been milled)
and configuration where the manifold mounting flange meets the top of the head.
Earliest heads have two curved (cast) dips between the center headbolt boss and
adjacent machined surfaces. 72-73 heads have only one dip on one side of the
center headbolt boss. 74-75 heads have a 90° edge all the way along with no
dips. These are the best. You might get some inference also if it has or
does not have the drilling for the water-heated auxiliary air valve (about a 3/4"
hole with a ¼"-20 UNC bolt hole on each side. The 74 and 75 models used the
CIS injection system and their auxiliary air valve was electrically heated.
Most B20F heads are 87 mm thick (=3.425") while the E heads are thinner at
84.9 mm (3.342") but otherwise pretty much the same as the B20F head, at least
on visual examination. (Higher compression ratio.)
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George Downs Bartlesville, Heart of the USA!