It´s like night and day.
The TBI units are normally massively flowing units that are clumpsy(sp?) in apperance.
A "standard" injector is basically set up for port injection work,whilst a TBI injector is what you might call an "electronic carb" kinda deal.
This also shows up in the OEM linepressure settings.
A TBI unit normally comes in at about 9-13psi and a standard one ranges from 35 and up.
All in all these are two different creatures.
Likewise the TBI unit will take a special housing for a fuelrail while a standard one connects to a fuelrail either via an o-ringed firring or a hose.
As far as i know the TBI units are high impedance units all the way,the standard injectors can be had as high or low(satured or peak and hold)
The list goes on...