Some more notes on using alternators for charging, that I forgot.
The alternator must be running in the correct direction so the cooling fan works correctly. That is usually clockwise looking at the pulley. This is important as it is running full output if relying on it self controlling the current, and it is important to run it at up around 6000 RPM as that is recommended as a good speed for full output.
The old Bosch alternators had a reverse direction fan available if you really want one. I have the part number filed somewhere. Putting the alternator beside the motor is a more compact layout !
I guess the reason for making your own charger is really that you hope not to have to use it much ! I would spend any excess money on panels first. Just the occasional use during the rainy bits for the genny, so it seems a waste to spend much hard earned money on something you will keep in the shed. I intend to make another one for that purpose soon. For my 24V battery bank and I have a 12V 120A Bosch alternator put aside and a 5HP Honda also. This time I will use a different excitation I think which will give better control. A PWM DC motor speed control unit.