Re: Easy HP out of 258?
You already have the easy horsepower. How much do you want from a 258ci inline, pulling a 4000 lb. truck with fat tires ?
There are lots of little things you can do, (like mentioned above) but you can only gain so much with a clumsey little truck motor. Everything you do to add HP on the top end is going to cost you torque on the bottom end.
I went thru this 20 years ago with a ford 6 header/intake/carb/ignition/cam... It made power, but for the same money, I coulda had a V-8 with another 100 hp. and alot better design. The old saying, "There's no replacement for displacement" rings true, thats the limiting factor here. A larger engine in a mild state of tune will be less tempermental, more durable, and less hassle.