Be a little careful with the very high current rated alternators, there's only so much that can be achieved with a given frame size on alternators, and usually higher peak output comes at the expense of output at low speed. There's a speed at which the alternator produces no usable output, the curve then rises fairly steeply up to around 90% at maybe 50% full speed, and rises to full output at near maximum speed. The zero amp speed is usually well below the idle speed, but is brought higher by rewinding for lower stator resistance (needed for higher peak output), meaning that the idle output can suffer. If you need significant loads at idle, about the only thing you can do is install a larger frame alternator or a dual install.
Don't worry about engine speed dropping a little as the alternator is loaded up, it should recover, what is to be avoided is the output voltage falling, that's the indication that the alternator has reached its limit.