Sorry exe, I'm with falcon on this one; a billet flywheel & heavy valve springs are only useful over 5000rpm, there are many other cheaper mods that will be more useful at lower rpm.
Start with hi flow intake & exhaust.
The effective range of a cam depends on the profile. Some cams only work at high rpm but, there are cams that only work
up to 5000rpm, meaning, you get a lot more bottom end torque;
for example... Unfortunately, that particular item is only available in Australia but, I'm sure, if you look, you can find one locally