There really shouldn't be that much oil left inside it but would be worth removing the sump plate while it's right way up as that forms the lowest point for oil to collect in during running for the oil pump to suck up.
If you're not wanting oil running out the bottom, take sump off and clean, leave motor to drain, refit sump so you can flip the motor.
Once upside down then the only way out for the oil is through the breathers as far as I can see, so fit pipes to those so you don't get oil dripping out and running onto the cases.
The camshaft sits in little pools of oil within those cam carriers on the head so you may get a small volume from those that haven't drained down when it was the right way up (it's design tries to keep oil there when the motor is switched off to avoid dry cam lobes before oil pressure builds) that will exit through the top breather.
It should do it no harm to leave it upside down as far as I can see.
