the deeper you're pockets the more HP you can squeeze out really, depends on your budget.
The basic is induction, combustion and exhaust.
So a good induction kit like the BMC system or another closed cone element would be perfect, if not, then a good panel filter (K&N, pipercross, green filters) alongside a drilled and de-restricted air box and a cold air intake would work well.
For combustion, you want some lairy cams, decent spark plugs, and stuff like porting and polishing.
For exhaust, you want a 4 branch manifold combined with a s/s system.
Throw in a decent remap and you should see something close to 200 horses.