Why are 318's low HP and torque?

Boy, just read this entire thread for the first time.
Here is my deal, I have a bone stock 1968 318,in the car and runs good. 80K on it.
Now, I just got the car and want to pep it up a bit, for street & hwy only.

I have options on two motors, both needing rebuilds. A 340 & a E58 360, I can be satisfied just adding some items to the 318 over rebuilding a non running engine.

I want a aluminum intake - Which one ? Performer, M1 or Weiand
600 edelbrock carb-have already
Cam shaft & lifters - which one?
Do I need to do anything to my heads? cut or etc. they are stock 68 heads

I have a 8 3/4 with 3.23 SG and Dougs Headers with full 2 1/2 exhaust w/H pipe.
Stock 904 & converter.
Lets see what you reccomend for me, the rebuilds or keep what I got. I am not looking to race, just a good rumpity sound and smooth performance. As you know its easy to dress up a 318 and most wont know it's not a 340 or 360.