robert1952:
I thought ‘post 73’ only applied to the 3MW/5MW. Nonetheless, the headlamps should be our guide with regard to the 6MW! Perhaps we should start new threads to clarify the new classes. 
Robert
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…or put them all in the same thread, to ease the process of comparison. 
ERF:
The 4MW cab continued for another circa 18 months and seems to have retained the 5-3/4 inch headlamps so far as I can tell.
I wonder if the “carry over” 4MW mentioned above is identifiable by having a mix of 4 and 6 parts? I refer again to the Doyle tractor, with its large lamps in 4MW-type panels. That statement disagrees with the above, though… 