Jacky,
It sounds like your application may not be a good fit for the ADM1270. Since the ADM1270 is designed to work with PFETs and not NFETs. This limits the number of FETs that are suitable. If the current limit threshold is 40A, the power dissipation in a 0.01 ohm FET will be 16W. The total power dissipation in the two FETs will be 32W and will be very difficult to remove the heat without bulky heatsinks.
I have only been able to find one 60V FET with a 0.01 ohm on resistance. These FETs are about $4 each and you will need at least 6 FETs to reduce the power dissipation to a more manageable 5W.
The board layout is totally dependent on the FETs since they will dominate the board area.
At this time there is no ADI SimPower tool but there is an Excel spreadsheet you can use to select the component values. You will also have to plot your operating point on your FET SOA curves to ensure that you do not violate the FET SOA.