Hi there,
For what it's worth, the A4 compressor on my Astrovan is mounted on "top" of the engine. It's actually mounted on the accessory mounting plate, which bolts to the front of the heads and block, but is above the block itself. I believe the one on my S15 pickup is the same. Interesting advice, probably a good thing to keep in mind. An AC guy I trust says to use Sankyo compressors as they last longer than the A4 compressors. I don't know from personal experience, though... the A4 compressors on my rigs all work ok, just are noisy in hot weather.

Regards,
Richard Wooldridge