surfacing cylinder head joint surface

the old seal has left marks...do i need to remove all before setting new gasket ?
I use sand paper on a glass to remove these marks but i dont want to remove too much material;
Is that enough like this ?
Plus, I notice i remove more on the sides than in the middle , the head is not perfectly straight...
Last photos with the second head to prepare...

It's generally ok so long as you can't feel any marks

It needs to be flat though, I'm not sure what tolerance is that the HG will take up

Have the heads skimmed this will eliminate any doubt that they will leak due to distortion.
There are limits to a gasket and iron heads can be quite stable when removed from a block but I would have them checked and skimmed.

If you skim then you need to check the rocker tolerances to ensure valves open and close properly. Shims are available

I used to check heads were flat with a thick piece of plate glass and engineers blue

+1 on check flatness. If you don't have plate glass & engineer's blue, the use an engineers steel rule. Plenty of videos on the tube showing the correct method(s).

If they do need skimming, make sure they do the inlet manifold face as well, otherwise the manifold might not line up. The V8 is 90deg block, so the heads will need the same skim on both surfaces. (P38 V8 heads have a 0.5mm / 0.020" skim limit, but not sure about the older 3.5 & 3.9 engines.)

You will need new shims for the rockers as stated above.

And all that wont make a difference if you have a liner problem.
Dont ask me how I know .

That needs to be checked.

J

the heads were already skimmed 10 years ago.I check with a plate and 0,05mm gauge, seem ok.
i have to sand the inlet manifold too...
should i stay with 400 paper or finish with 800 ? i have a metal gasket.
Thanks.