Specs include:
Voltage: typical choice is 120VAC or 230VAC.
Power: as you state, 80 kva, or else 80 kW.
Speed of rotation needed to produce your desired frequency.
Typical choices are 1800 RPM or 3600 RPM (in the USA). It has to be compatible with your engine's power characteristics. If your engine is governed to operate at 1800 RPM, do not choose an alternator which needs 3600 RPM to put out your desired frequency.
Output connectors: You want this to be compatible with your power distribution system.
Instruments: You probably want meters for voltage and current output, at least.
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Also:
Method of connection to engine.
Structure to support weight of alternator.
Who will install, attach, troubleshoot the system? If you pay someone to do this, what sort of warranty goes with the equipment?
Do you want new equipment? Or will you accept a good deal on used equipment?