how feasable is it to swap an evo 3 motor into a spyder and turn it into a gsx. has anyone ever done it before? please write me and give me your input. it will be greatly appreciated...

 

It has been done before. Dont bother with an EVO III motor. Just find a wrecked GSX, pull the drivetrain parts off it and thats all you need.

 

The time, money, and effort to find a complete JDM EVO3 motor, is not as easy as looking online for one. Sure, you may find one, but finding the actuators for the Cyclone intake manifold (if the ones you buy are faulty or just broke) will be a tough find, unless you got through the dealerships...in Japan. You can probably order them through local dealerships, but they may not even have the part number because it's not one that's carried in the states.
...and there's the only difference right there...the intake manifold. That just doesn't justify the headache, IMO.
There's nothing wrong with the US motors, it's an older version of the newer Eclipse/Talon 4g63 with the same issues of the 2G bottom. With that said, I recommend a 1G bottom and 2G upper or a straight 1G motor with the correct ECU and wiring. It's not like you have a Mitsu Mirage and want to convert it to a left handed EVO3....