Please post some pics of your EML Airhead. I am building up a R90/6 powered Wasp Replica.
What are you changing over to Oilhead? Engine only, Engine + Gearbox or complete drive line?
You may find the offset of the drive output shaft differs about 30mm (?)
if you were going to run the EML airhead swingarm in the back, you would either offset the motor in the frame to line up the drive shaft or move the right pivot out to the right to compensate. That is what HPN do to their airheads with a Oilhead swingarm, you would already know this.
If you are running the complete drive line then its a matter of measuring how much width you have to play with. Being a sidecar it shouldnt have too much impact.
Oil cooler, the bigger the better with a thermostat.
Oh please post build pics