Give this a read:
Injections per Engine Cycle is set the number of squirts you want per engine cycle. You want this to be set so that your idle pulse width is no less than 2.0 ms, if possible, and your Req_Fuel is less than 12-15 milliseconds, but more than 8 milliseconds. These values allow proper tuning of the idle mixture while maintaining the ability to apply enrichments (acceleration, warm-up, etc.) under full throttle. This is the total injector events that you wish to occur for every engine cycle (360 degrees for two stroke engines and 720° for four strokes).
Injector Staging values for injector staging are simultaneous or alternating. If you want all your injectors to fire at once, select simultaneous. If you want half your injectors to fire at each injection event, and the other half on the next event, select alternating.
Note that with port injection, you must choose at at least 2 squirts per cycle with alternating injection, otherwise every other cycle for each cylinder will get NO fuel! The engine will run very badly.
There is some benefit to choosing 2 squirts/alternating for port injection, since only half of the injectors fire at once, the pressure drop in the fuel rails is reduced and the fuelling is more consistent.
With throttle body injection, the number of injection/cycle you can will depend on your number of cylinders, plenum size, Req_Fuel, etc. You have to experiment to see what works best for your combination.
Engine Stroke values for engine stroke type are two-stroke or four-stroke. MegaSquirt uses engine stroke to determine how many degrees are in an engine cycle.
Number of Cylinders is the count of the cylinders on your engine. If you are unsure how many cylinders your engine has, you should not be installing MegaSquirt on it. This value is actually the number if ignition events per cycle sent to the ignition input on the controller.
Injector Port Type is used to select the type of injectors that you are using, throttle body or multi-port.
Number of Injectors is the total number of injectors MegaSquirt is controlling, whether port or throttle body injection.
Source:
http://www.megamanual.com/v22manual/mtune.htm#constants
Let me know if this helps!
Steve
Thats right. The 3vz-fe had 180 or 200 hp, depending on model. No mechanical differences between the two, just map/ignition differences. 
