Not sure what you mean by a '30 over 318' and '4.04' as those are not the same thing. As for bore, there is no way I'd go to 4.10 if it required any block fill. Leave it smaller and you'll never know the difference.
yep. X block comes 3.91 ish bore. So 30 over would be 3.94
They usually will go 4.070 with no issues. I had one i ran at 4.100 and had enough at that bore for a freshen with a custom piston( would try to avoid going all the way out to 4.125)
I am not a concrete in the block guy, so I prefer Lots of meat and not a questionable bandaid