Need 318 help/advice

Pressure is power, especially at low-rpm.
Consider how a diesel makes low-rpm power, with a fuel that has less energy in it per pound than does gasoline.
Or how does a turbo/supercharger work? It stuffs more air into the cylinder so you can add fuel ...... to increase the pressure.
The very last thing you want to do to a gas engine destined for street duty, is to reduce it's pressure.
This goes triple for a low-pressure 318.

The fastest way to lose pressure in any engine, is to bolt on some bigger-chamber heads, and the second fastest is to stuff a cam into it that has a later-closing intake valve.
These are the two things that most often get done to a 318. And these two things; with no other changes, when done to a nominal 8/1Scr 318, will immediately make the bottom end (say below 3000/3500rpm) very very soft.
It sorta worked, back in the day when the 318 was a nominal 9.2/9.0 engine , because we had never even heard of 2.20 or 2.45 gears, and our 318 cars already had 3.91s/4.10s because that was the fastest way to performance, back then; and we all knew it. So the next step was always to bolt on the 340 top-end.
But that crap don't fly for a Smoggerteen, that altho advertized at 8.0 Scr, never was, and when you take out the .020 318steel shim gaskets, and swap in .039/4.18diameter composites, it only makes a bad situation so much worse.

Now, your 1970 model 318, probably came with a 9.0 Scr so that would give you some wiggle room. But that was 50 years ago so who knows what Scr it is sporting today, which is why I suggested to start with a Compression test ..... to see how bad it really is.
If you had a true 9.0 318LA, your Total chamber volume would be ~81.5cc..
Just the headgasket change will add about 5cc to your total chamber size. And say your valves have receded, adding another 1.5cc; and so the total chamber size has grown to 88cc.
The net effect of just these two, is that your 9.0 engine is now, just 8.4..
Given this as gospel, your 318LA at sealevel, is likely to make about 147psi.
By a more typical elevation of 800ft this has dropped to 143 psi. Now there is a performance factor that combines pressure and volume, and spits out a whole number that is useful to compare engines of various displacements, as to low-rpm performance. In the case of the 8.4 318 at 800ft, the formula spits out a P/V of 118.. Read about it here;
V/P Index Calculation
Adding the X-heads at 72cc, over the 60cc 1970, 318LA heads adds another 12 cc . Yes 12cc.
Your new Scr with a total chamber volume of 100cc comes to 7.5, and your pressure is predicted to fall to 123psi and the P/V to 101. That is equivalent to a 14% loss of low-rpm performance

Next; lets install that 340 cam, with it's Ica of 64* (compared to the 318 cam at 50*). The pressure falls to 101psi and the P/V to 80. At P/V of 80, compared to a starting P/V of 118, you are now down 32%
BTW P/V of 80 is LESS than a stock 225 slanty puts out.

I don't care what anybody tells you; with no other changes
this is exactly what happens in real life; your 9.0 advertised 1970 318LA will turn into an azz-dragging turd, until that 340 cam starts waking up at about 3800 rpm.
With 3.23s and 26" tires, that is about 31mph
With the stock TC, that mightabin a 2200@PV of 118; but might now be a 2000@ PV of 80, it will just be a horribly embarrassing turd of a combo until it gets to around 3800rpm.
I have done this just once for myself, and twice for idiot buddies, at their insistence, and can testify to the lunacy of doing this.
And there have been several FABO members over the years, that have been brave enough to step forward and concur, that this is what happens in real life. And the only way to band-aid such a sad situation is with a hi-stall TC and "race gears" like 3.91/4.10s .


BTW
A good P/V number is 140 or more. But I don't think you can get an iron-headed 318LA up there, and still be able to floor it.... with a 4bbl..