Hi Rimmer, thanks for your posting - yes, the 72 is derived from the 52 but this also had a gimbaled (not fixed) platform. Those days all these systems worked like this for some reasons (1) the instruments are much more accurate if they are not rotated throughout the flight as e.g. each accelerometer also measures a little of the rotation. (2) Computation was much more easy if the accelerometers measured N/S, E/W and Up/Down - so one stage of transformation was omitted in this way. (3) Just by routing the signals from the platform sensors via buffers to the plug of the unit, attitude signals are available which are very accurate and for free - these where used in the attitude indicators etc.
The later carousel units slowly (minutes) and constantly rotated the platform with the instruments thus averaging out any bias in the N/S and E/W accelerometers - that was a really clever idea... Have a good time, Erik.