[MA70-3.0GT]

Sorry to say this, but as far as I can tell from the pic what appears to have happened is the previous HG (guessing it was done fairly recently) went in the same area & somebody was a bit over zealous with the cleanup of the affected area. TBH it looks from the photo as if it's been hit with fairly heavy sandpaper or wire wool... And then the resulting block warpage has given the effect we see here with the next HG.

I'd have to agree with cre that machining is the only sure way to make sure it's within warpage tolerance, the head may also need skimming now if that's in a similar state. As to modifications after a skim, it depends on how much material is removed & I can't think of the specs off hand but it's in the tsrm anyway & if both head & block come within the tolerances after skimming then you don't need to do a thing.

However if (as usual, as the factory tolerances are tight-ish) there is too much material gone for a stock HG you can go for a thicker metal HG to take up the difference, you'll need to look into head/deck finishes for that route though as they have to be mirror like... IMO best have the pair finished to MHG surface roughness specs from the get go & then if you find you can get away with a stock item (if you really wanna by then!) fair enough, but if not you're not stuck then with running back to the machine shop for more sessions & more material/not to mention cash, lost...