The 744F new from Boeing has a layout like this:- Looking rearwards from the flightdeck, galley on the right then a door leading downstairs then 2 business class type seats. On the right is the toilet then 4 business class type seats. At the rear of the last row of seats is a door leading to two bunks. The ladders onto the main deck on the 744F from the upper deck arrive on the main deck near the port side of the aircraft.
On any converted 744 the upper deck can be any one of numerous layouts dependant on where the aircraft came from i.e if it was formerly a passenger aircraft with a stretched upper deck then the layouts are endless!
As for 742F's, the ladders from the main deck do indeed arrive on the main deck in the centre but the main deck layout caters for this with one pallet position to the starboard side of the ladder although the ladder can be folded upwards to enable easier loading/offloading.
regards clive.