1996 sierra HELP!

I have a 1996 GMC Sierra 4x4 regular cab, short box. It has a 4.3 liter vortec v6 that is supposed to put out 200 horse power. Would it be possible or even economical to put a 5.7 liter in? Would it fit easily or would i have to change a lot? Would it give me much more power than my V6 that has a kn air filter? Would it give me enough more power to make it worth while? Gimme some advice please... thanks