I've gone for a Revotec 10". It's being sold as suitable for an Escort MK2 so will assume with the greater cooling capacity of the Morgan it will be more than sufficient. If I mount it high on the radiator, I think it will just clear the crossmember - there's about a 46mm gap at the moment, and the deepest part of the fan is 51mm (which should clear above). If not, I think I've got enough wiggle room to move the rad 5mm forward easily.
Not sure about fitting - I'll see where it sits, and what metal work is around. They sell a couple of metal side plates that I reckon will work with a couple of U clamps or similar.
If it all goes in OK, will fit one of their adjustable thermostats into the top hose (although it will mean cutting my lovely new silicon hoses!)
Will probably keep the fan in the back of the car as a emergency back up.
