i have pics somewhere, [but maybe not on this 'puter] but i just looked on the shelf to confirm my memory.
i believe that housing could be a 392 hemi. they have the single hole inlets to the heads, and the single large upright [not the heater hose barb] barb is a bypass to the intake manifold.
what size diameter is the water pump housing ? the hemi pump diameter is larger than a big block pump, which is roughly 5" [ish].
a front side pic of the housing, along with some measurements [like bolt hole center to center, etc.] will confirm my suspicions.
edit : the casting numbers on the housing do not match anything i have on the early hemi, however. this still doesn't mean that housing is not for an early hemi. measurements will help.
another thing. the early hemi also has 4 attaching bolts for the water pump like the big block, so now i just don't know what to think..........