I looked at the pictures (good pictures) and my previous warning seems to be the culprit. It appears that the head bolt was tightened on a hole with a liquid in it.
If I am right about that, it means that the structural integrety of the area is not the failure. This can be important depending on the level of fix that you want.
The cracks were not welded properly. The outside weld had no penetration. The top surface must have been notched and welded over and remachined down. There appears to be many porosity bubbles in the surface. This can be caused by all kinds of problems. The proper repair probably would be to notch out the whole area and rebuild with weld. I don't do that level of aluminum welding on blocks, mainly because of the machining requirements. This amount of repair would require the motor being out of the car, I would imagine. I only know one person that can do that kind of work. he is in Orlando FL.
The significance of the cause of the crack leaves the possibility for a partial repair. If the structure of the area is sound an insert could be put into what is left and the cracks should be no worry as they aren't in sealing areas. All that is necessary from that hole is that a head bolt be able to get proper torque on the head.
[Edited by Webmaster on 04-10-2001 at 06:25 PM]