360 Aftermarket Heads on 318

Performance is not really about compression ratio; rather it is about cylinder pressure.
You can install any number of different cams into a 9.5 Scr engine and get pressure ranging from in the basement to in the attic.
For a streeter;
The pressure is what makes a snappy street engine.
That 7177 Edelbrock cam may be fine in an 11.5/1 engine, but in a 8.0 engine she will be a slug.
This is why bolting on big open-chamber heads onto a stock low-compression engine is bad enough, but if you then add a big cam, Bam! you get a dog of a combo. Sure it might make half decent power once the RPM gets up, but now you are committed to running race-gears, and a hi-stall convertor.

Here's an example.
Say your 9.2Scr early 318, with the stock cam (240/248/112) pumps 158psi. That's getting up there, Street-Performance will be pretty good.
Now say you install heads that are 14cc bigger.
At 9.2, the total chamber volume was 79cc. So at 79+14=93cc your Scr is now 8.0 and with the same cam, your pressure falls to 131psi. This is about what a smog 318 pumps, which everybody will agree is already pretty lame.
Now install a 340 cam (268/276/114) and the pressure falls to 114psi which makes a really really lame low-rpm engine. Couple that with 2.76s and hang your head in shame. I did this so I know this. It took 4.10s and a 2800TC to get outta that hole, just to get back to a normal bottom-end performance.
The 7177 cam is; 308/318/112, 234/[email protected], .488/[email protected] arms
But they don't publish the lift at 308* so it's sortof a useless number to work with;
The Wallace Calculator has been pretty accurate for me using the .006/.008 tappet rise numbers that most popular camshaft grinders supply. But in the case of the Edelbrock, not having those, I can only guess. Typical hi-performance cams will have acceleration ramps of 46 degrees or more, some as high as 53. Lets say I guess 50*. That would make the comparative numbers to be 284/294/112 advertized at .008 tappet rise. which is typical for this size of cam. From those numbers;
YOUR pressure in a 9.2 318 comes to ~130psi.
but if you install heads with 14 more cc, making your 9.2 engine into an 8.0 engine, then the pressure drops to
get this;
108psi.
And that's if I guessed at Edelbrocks .008 advertised correctly. The pressure could be lower.
At this low pressure, this 318 will have bottom-end power that is similar to a 225 slanty. This 318 will not wake up until deep into the 3000s rpm.
Now, all these examples come from the Wallace Calculator, input to 1000ft elevation..

So, as you can see, or should be able to see, pressure is a really really big deal.
However it has a downside, the more you run, the more likely the engine is to detonate, which breaks engine parts. So there is a limit as to how much you can run.... at WOT.
Typically, with iron heads, and on the street, the limits are; 165psi for 91gas, 160 for 89, 155 for 87octane.
Closed-chamber heads running a tight Quench, may go a lil higher.

My message to you is this; that if you bolt on big chamber heads, and then install a performance cam; you will be in for a very rude awakening.
There are way better things to do to that combo, that do not involve going into the engine.