318 build check from you experts

Spokane/Elevation

Spokane is located on the Spokane River in eastern Washington at an elevation of 1,843 feet

Do yourself a favor and go find a 360/5.9

Or else prepare for a lotta rear gear and at least a 2800 stall. Both of which at your weight will kill fuel economy.
Your 318 will not get much out of alloy heads; but they will be killer on a 360, in your application..

Here's why; at your elevation, getting the pressure up with a 318 is very difficult and expensive.
A) Suppose you get it up to 9.0Scr, and suppose that your 252 cam has an Ica of 54*. The end result might be 150psi with an
Effective Dcr of 7.5@ V/P of 121 a pretty weak bottom end
B) Suppose you get her up to 9.8 with closed chamber heads and a tight-Q of .040 or so. Now the pressure might be 164,This is about the limit for 91 gas and iron heads.
Effective Dcr is looking like 8.0 @V/P of 131, still a weak VP.
C) ok but suppose that lil 252 cam doesn't cut it, lets try the 268/276/114, 340 cam that everybody is always bragging on. At 9.8Scr and an Ica of 64*, the pressure falls to 149psi, the Effective Dcr to 7.45 and the VP to a less than mediocre 110. And this is at Scr of 9.8! This is so doggy off the line, that you will hate it. To get the VP back up to a reasonable/but still low 131, the Scr needs to be 11.2; that ain't happening. To get 11.2 at 3.93 bore the Total chamber volume would have to be reduced to 64.6cc. Since you will have to run the .039 FelPro gaskets(8.8cc) to deal with the pressure, and the Eddys are 63cc, you are already up to 71.8cc!, yeah so custom pistons it has to be, and probably machining of the decks and a matching cut off the intake; read very expensive. With iron heads you would be dead in the water

D) Ok but the 360 with KB107s, Edelbrock alloy heads, and an .028 gasket, will come in very close to 10.7Scr, with no machining besides for the pistons, read cheap. Now; your pressure with that 252* cam, jumps to 184psi, your
Effective Dcr to 8.75@ a V/P of 156, which is funtastic.

So what you didn't spend on milling stuff, you can put towards a 360/5.9 core, AND you can keep whatever gears and stall is currently in the truck, for an even bigger savings,
AND you can run 87E10 gas for a lifetime of saving money.

Because of the very high V/P,(156), and the alloy heads, you could theoretically run a bigger cam now.
I suggest a 268/276/108 with an Ica of 60*. This will only sacrifice 2.5psi so still 174.5, the Effective Dcr drops to 8.76, and V/P only falls to 141, still a ton of fun. I would not run any bigger on the street.
I have, in the past run about this same pressure/VP combo at 930 feet.Yes on 87E10.
The 268 cam is about 2.5 sizes bigger than the 252, so the powerpeak has moved up about 500 rpm from something like 4500 to 5000. With the 275s (88" roll-out) you can use 3.23s with this and hit 60=6200/6300 10% slip........ still in first gear,lol. and when cruising 65=2520@ zero slip, perhaps 2600 on the tach.
Read about V/P here;
V/P Index Calculation