Is there a difference between the Escort Cossie head and a 2wd head? If so what is it

 

quite a few differences

thermostat
damper bracket is missing from a 4x4 head
all the heads are interchangable but it will affect comp ratio slightly
The 4x4 head has an oil feed in the side of the head by the turbo

it really depends on which way you are changing, e.g if its a bare head then 2wd cams wont fit into a 4x4 head