what is the difference between an ef xr6 engine and a plain ef engine and can you tell the difference just by looking at them?

from the head gasket down they are all the same.
the head and cam is different. you see a large T cast on to the front of the head, tickford part numbers use "DA" ford numbers are normally "AA", "AB", thats the basics of it and enough info for you to identify the tickford head/engine

sweet as man thats been the most helpfull

The T is hidden by the plastic belt cover on the front of the motor, though it only takes one nut and the power steering pump cap to see.