All engines have limitations on the amount of torque that can be taken from the front of the crankshaft. Exceeding the torque limits may cause damage to the front main bearing or even the crankshaft itself. If that torque is taken off by means of belts, then there may be restrictions on the amount of torque in particular directions, and there might be restrictions on the allowable distance that the pulley (s) may be located from the front of the block.
In the case of the D2-40 engine the max allowable torque is 21.7 Nm (16 Ft.Lb.) in the direction that your belt is pulling. This translates into about 9 hp allowed at 3000 RPM
or 4.5 hp at 1500 RPM
. This amount of power can be taken from one pulley (assuming the belt size can handle it) or split among several pulleys as long as the distance forward from the standard pulley doesn't exceed three pulleys or a combination of spacers and pulleys of the same thickness.
As mentioned earlier, the combination of a flexible mounted engine and a fixed belt driven load isn't a good thing. It might be that normal engine vibrations wouldn't cause problems, but motor
sailing into a nasty chop could cause the engine to move around enough to place excessive loads on the crankshaft. Some sort of spring loaded belt tensioner might be a good idea.