You can easily run boost through a stock KA motor. Easily. How long it runs and how well it runs has everything to do with the current shape of the motor and the tune itself. Detonation kills motors. If you're unfamiliar with detonation, also known as knock, you should read this, detonation and preignition
How you attain 300whp will also make a huge difference on things. What I mean by that is, yes you can make 300whp by just cranking up the boost and adding fuel. But it will be much harder on the motor than if you were to have a proper set of cams, a good flowing turbo manifold, the proper cooling modifications and a turbo that is operating within its realm of efficiency rather than screaming at 110,000 rpm trying to make more boost than it's designed for.
You can do it affordably and make a lot of power if you go about things the right way. To be honest, by the sounds of your first few posts you might want to have your car professionally tuned as that's an area where a novice will do the most damage. Trust me on this, I have blown up all sorts of things being stupid.
When my KA went I knew it had rod knock. I didn't think it was severe enough to lock up the motor, I was wrong and tossed a rod through the block trying to limp the car home. Should have towed it. Expensive lesson learned. My fault, not the motors. In fact, every motor I've popped has totally been my fault. I had lots of money, no kids and access to lots of motors when I was learning though. So unless you're willing to blow stuff up and swap parts left and right, make sure you know what you're doing.
Sorry I'm late to the party.