There are a lot of ways to increase HP and I guess the big question is how you plan on using the car / motor. If you're doing it for full race intentions, you would probably go with a very aggressive cam (a lot of duration and lift), high flow cylinder heads, and an intake manifold to match the heads flow. If your intent is to have a car that is primarily a street driver, with an ocassional run on a 1/4 mile strip and or road course, you would probably go for a street / race cam (less duration and lift, better idle), and the appropriately matched intake manifold and cylinder heads.

You also need to address the carb setup that will be feeding fuel to this more powerful motor. I just went through this same exercise to "tweak" my 302.

I ended up doing the following which will take my stock 302 HO motor (225-230 hp) up to 350 HP at 5800 RPM:

-Aluminum cylinder heads. Was going with AFR 165's (you would
probably need the 185's) until Unique told me I would have to
modify the exhaust system to use AFR heads (this was based on a
car they built for someone using AFR's..they had to modify the
exhaust headers ). They recommended, instead of having to modify
my headers, to go with either Trick Flow or Edelbrock. I went with
Trick Flow Twisted Wedge heads, bought via Panhandle Performance.
They buy the casting, use better valves than stock (Ferrea racing
valves), polish the bowl, use upgraded springs for my roller cam,
and the result is a head that flows better than the 'out of the
box' version. Turns out that the AFR 165 and 185 heads CAN be used
without modifying the headers, and it is the larger AFR's that
require modifying the headers. I have the new TRick Flows on my
desk in the den, and they are beauties. Can't wait to get them
installed in the next 2 weeks.

When you switch from iron heads to aluninum you can run a full
one point more in compression as the aluminum, which has faster
heat transfer characteristics, burns cooler. "iron heads make
more power" is a quote you will come across. In order to pick up
a small additional bit of compression I am not using the normal
relatively thick Felpro gaskets, but a much thinner racing head
gasket (costs $125 a set instead of $45) that is about 20
thousandths thinner, this gives the effective benefit of milling
the heads to slightly decrease the size of the combustion chamber
and increase the compression slightly.

-Intake manifold. My motor had an Edelbrock Performer RPM intake
manifold, and it flows well enough for my 302. Your motor migh
take something a little bigger. Key is to have the flow
characteristics of you intake matched to your cylinder heads. Too
much Volume flow capacity in the intake is not good because then
the velocity may drop, which can cause the air fuel volatized
mixture to separate. Velocity of flow is very important.

-Camshaft. This determines how everything works. The guy I would
recommend you talk to does nothing but grind cams. Jim Dowell
of Racer Brown Cams in Maryland. (410) 866-7660. My stock HO cam
has 209 duration and .444 lift @ .050. I am going with a new one
that has 221 duration and .500 lift @ .050, not an aggressive
cam, more duration (valves are open slightly longer) than my
present cam, and about 60 thousandths more lift, so the valves
open more to let in more fuel / air to the chamber.

-Carb. Having the righ carb and having it tuned properly and
timing etc. set right are critical to be able to get the desired
performance from all of the above. Don Gould in Washington
(web sight is 4secondsflat.com) is THE man. (503) 627-0728. Don
will take in all of your engine, trans, rearend, etc. specs, and
he will recommend a specific Demon carb. He will not have it
shipped from the factory, but for $25 he will receive it as his
shop, he will tear it down, and rebuild it to be sure all of the
parts are correctly intalle