The high output current/power you specify is making the design a bit challenging.
I would consider dividing the task in two halves: First, constructing an isolated converter with specification 16-24 V input, output controllable between 16 and 8 V, 32 A. Then "adding up" the voltages by connecting the "negative end" of that converter to the positive input rail (which you said is 16-24V), and controlling that converter's output voltage in a way it always adds up to 32V when summed up with the input voltage.
That way the converter's topology can be made to be more suitable for high currents than the usual "flyback-boost" regulators, storing all of the energy in an inductor, and having very high current peak values and thus also extreme ripple currents. Very high peak currents and ripple makes the practical implementation of flyback-family converters extremely challenging on high power levels.
There are many good articles and Application Notes around for switchmode DC/DC converters, for instance Microchip AN1114:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en532115 . Our friend Google will bring you to many more with suitable keywords (such as: high power switchmode converter application note -- and similar wordings)
Of course, all output power might pass through the converter instead of connecting it in series with the input, but then it will be nearly twice as large ( about 1024 W versus about 512W ).
The current limit may need some consideration, but if a "fold-back" type operation is OK, you could even use a series (mosfet) transistor as an automatic circuit breaker -style current limit. Easy to design, and easy to make very robust and reliable.
