Everyone keeps saying its been tried and it didn’t work or it is too expensive. There have been a lot of advances in manufacturing technology that makes things possible today that weren’t possible before. An economical and reliable integral head/block can be made, but only in an inline configuration. V engines probably could not be done with todays technology though horizontally opposed engine might be possible.
The engine would not be cast, that would be too difficult/expensive. It would be mostly aluminum. The first piece would be a block of aluminum that is pressed to form the combustion chamber, bottom floor of the water jacket and the outside jacket of the block. Pressing this eliminates a lot of the issues with casting.
Then the intake ports and exhaust ports are cast and set into place. The top half of the water jackets is pressed and then placed on top of the block/head, sandwiching the port runner in place. It is pressed into the head/block to pressure weld the two pieces and the port runner in place.
A one piece Iron/steel sleeve liner and upper bearing web is made. The sleeve liners also serve as the inner water jacket walls and the bracing that holds the liners together serves as the bottom of the water jackets. The pistons and crank are assembled and a lower bearing web is used to bolt it all together. Then this is inserted cryogentically into the block/head assembly.
Holes will be made through the head for the valve assemblies that would screw into place. The valve assemblies would of course be solenoid actuated so cams would be unnecessary. Machine in sparkplug holes and finish off the engine conventionally.
The engine would be essentially un-rebuildable but with most engines good for 200k or more and a lower cost to manufacture, that should not be an issue. The valve assemblies would be replaceable in case one of them went bad, but other than that, just routine maintenance.