are you allowed to mount the compressor on it’s side?
Yes. you can.
An example: http://www.seadawgs.com/Pictures/2002/Construction/2-17-02/betaframe.JPG
Answer supply by Bill Gold from 258
The rubber shock mounts don’t work very well when the compressor is on it’s side. I would check the manufacturer to make sure that there is not a problem with lubrication of the pump internals as well.