I've done the oil change now, I did it the conventional way with the drain plug. My main reason for considering the syphoning route was ease of access and reluctance to use axle stands. I sorted out those issues, but the job was still a faff, as the convertible has a metal undertray held in with 20 ish bolts! I didn't run the ford oil through it, just went with the Mobil 1 esp.
Glad I did it the right way.