HRS:
Morning Spardo,
AEC & later Leyland liked the front end crankshaft mounted PTO to drive the drum ( had to be turning all the time)
later they settled for just the big bump not the whole bumper job as in the picture.
Foreigners liked the gearbox driven PTO’s quicker, cheaper and no need to have a radiator with a hole in it etc.
Bet you wished you never askedHarvey
Not at all mate, very interesting, I had never seen that version and at first thought it was a distortion or optical illusion in the picture. One of the few things I have not driven (others are car transport and liquid tankers), mixers, too much paddling in and out of the cab in muddy boots for my liking. 
Just had another look, were those vents on the top of it or something to take weight, such as a driver cleaning the top of the screen for instance?