There are a couple of serious flaws in the alternator cacl worksheet.
Unless your alternator has a "smart" multi-stage regulator you won't get rated current out of the alternator at "zero load" for very long, a few minutes maximum. The standard voltage regulator will start reducing the current as the voltage comes up. By the time the voltage reaches 13.2 volts the alternator may only be providing 20% of its rated output.
If you have a smart regulator (not common) then the regulator will hold the alternator at full output until the voltage reaches 14 volts, at which point the battery should be 80 to 90% full.
A second flaw is that the charge characteristics of a battery are not so simple. THe higher the current rates, the less the efficiency. It will take a lot longer than 1/2 an hour to recharge a 50% battery even if the alternator puts out a full 100 amps. This is also hard on the battery so you really don't want to do that.
The "bulk" charge will only take the battery up to something between 80% anbd 90% full. After that it needs an "absorbtion" phase that holds the voltage and slowly decreases the current to get the battery to 100%. A standard alternator used in this type of application may never fully recharge your battery.
Another thing to keep in mind is how you are going to spin the alternator. Larger alternators put a larger load on the belt. There is a limit to how much energy you can transfer from the belt and trying for too much will make belt life short and wear out bearings (because you have to make the belt really, really tight!)
100 to 120 amps is about the most you can get out of a single V-belt. To go above that you need to change pulleys and have double belts. I am not sure what the limits are on a serpentine belt.