Do domed KYB 399’s interfere with 302 cast heads?

IMHO,
you need to include your cam in the equation, cuz the ICA is gonna affect the Cylinder pressure quite a bit. Or viceversa, the Ica will require a certain window of Scr to achieve what you're going for.
On the Street;
Scr isn't necessarily what yur after.
Pressure is the thing, and the Ica is gonna play a big part in that.
Scr in this case, is just a means to an end.
If yur gonna run iron heads, you can quickly get into a bad situation. Especially with open chambers.

I run a 360, so it's a little bit different. But with closed-chamber alloys I can and have run 195psi, and if yur running an automatic trans, with a low stall, and you need bottom end, I can tell you that 195psi is killer strong. Typically, you cannot run much over 165psi with Iron heads and best pumpgas. Whereas I run nothing but 87E10.

If you intend to walk that hi-pressure line, with a 318; everything has to be just right, and everything has to be well thought out, including the chassis, the weight, the gearing, and the stall.
Usually, it is just easier to stall it up, and not lose sleep over the lower pressure.

Furthermore;
If you have a manual trans, you don't have the choice of stall, and many many times you are gonna find your engine at too low an rpm, where, with too much pressure, she will detonate; and to eliminate that you will have to sacrifice Ignition Timing, and when you do, away goes the power. In this case less Scr would/could have been better. Walking the line with a manual trans takes extra caution when a manual trans or especially when hi-way gears are involved.

Without knowing any of these other factors IDK how anyone can answer your questions; I certainly cannot.

One thing that is almost a given, is this; on the street; Flat tops are usually best as is a tight Quench. I have always run from .028 to .032, with alloy heads and hypereutectics, with no issues.
In a budget 318, where no machining is allowed, I'd likely run a Quench-pad piston, and closed chambers, but it really depends on the cam.
What I would not do is run less than 160 psi. What I'd like to run is 185 to 195psi, with alloy heads; but that's a stretch for a typical street cam with an Ica of say 61 to 66 degrees.

The thing is, with the wrong street gears/stall, there's no percentage in that either. Low-compression 318s on a budget are just hard.

Here's an example; say the cam you pick will have an Ica around 63 degrees. and say you are at 500ft elevation. To get to 160psi, the compression ratio wants to be, about 9.8 .
But to get to 185psi will need 11.1Scr. But to run that pressure, on the street with pump gas and full timing without some type of anti-knock, you would need alloy heads, and probably a tight quench.
However with a smaller cam even just one size say an Ica of 59*, Your pressures will jump to 164 and 193..
164 will require best octane gas. 193 may not run WOT on 87 gas.

So, in this case if 160psi was not enough for you at 2200 stall, perhaps 2800 would be a better solution, and/or, more rear gear, and/or less weight.

Sooner or later, you might conclude that you need 4.30gears, which then leads to an overdrive, which then runs well at 155 psi, and maybe she'll be able to run 87 gas.

It's all in the combo....... IMHO