Any specific reason behind attaining this 120hp mark?
Let me give you a little idea.
The 1ZZ-FE in Altis which is 1.8L produces around 130hp.
The 2NZ-FE in GLi produces around 84hp and its 1.3L.
With plugs and downpiping you will never achieve that much increase in hp.
Performance can be slightly improved with the addition of such minor mods but dont expect any thing near 120hp by doing these mods.