Hello. Your electronics from a prusa i2 will work just fine for a i3 printer. However, you will probably need to adjust some items in the firmware that you choose to use. I have some i2s and i3s, and I remember needing to change things in configuration.h like the INVERT_X_DIR, INVERT_Y_DIR, INVERT_Z_DIR, and INVERT_E0_DIR. You'll also want to slow down the z-axis because it uses M5 rods instead of M8.
Anita
3dbotshack.com
