You spelled "diesel" wrong in the title. If you can change that you should.
Also, you could add that it is a mechanical lifter head to the title.
The cracking between the valves is nothing to worry about (usually). It's only if the cracks are too wide that it can be a problem. I think the Bentley (service manual) specs it at the width of a penny. It's always a good idea to pressure test the head before investing in a rebuild because of this.