Why use a passenger side water pump housing?

When I built my first 440, I used a 1978 block and didn't even know that they used lefts and rights! I just used what I had.
I planned on using the radiator my 318 car came with so naturally, it just seemed right. Everything lined up as if I planned it.
Last year I switched a few things around to add A/C. This necessitated a change to the LH outlet and a new radiator.