Ohh thats fine.naturally aspirated means no forced induction (turbo, supercharger) and no nitrous

Heres a few:

Stage 1 or 2 cams
Adjustable cam gears
Retainers
Springs
Header
Maybe even a thinner headgasket to promote higher compression ratio (NA only)

Or if you wanna go bigtime:

High compression pistons (NA or nitrous only)
Lightweight rods
Port and polish the head
valves
engine sleeves (For making big power)

Hope this helped