Sorry Rob. Please excuse my frivolity :wink:
As Jim has said, oil filled compressors do need to be the 'right way up' ie sump at the bottom, oil filler at the highest point. If you have an oil free compressor, then you should be able to mount this at any attitude.
The receiver needs to have the drain cock at the bottom and the air take off in inlet points well above the drain. Oil and water traps in line, needs to be the right way up as do oil feed devices for tool lubrication.
If appropriate, then separating the compressor from the receiver with a short length of suitable pipe might allow you to re-jig things to your needs.
Hope this helps
Bob