GSXR400 MSP 1992

Hi guys. Been riding my GSXR400MSP 1992 for quite a while and feeling
a certain lack of power so decide to embark on some modification.
Things I am looking at includes:-

1. Air box modification
2. Able to do a "ram air" setup?
3. A aftermarket CDI???
4. Aftermkt full exhaust system. (Can't find any on ebay etc)

Any guys here who have done anything on their GK76 for power
improvement?
The bike controls really well so I don't think there is a need to
improve control.
Well there is any advice, I will most appreciate!

Hope to hear from the veterans here.

Thanks!

Kim