I was looking on your site to find the fix for the fuel leak on the back of a 24v head, which I did find and it was very well written and I found the info I needed and I appreciate the excellent write up. One thing I do not understand is the fuel line going to the back of the head. Please excuse my ignorance but what exactly is the purpose for that line? I'm sure you cant block it off but I was curious about what its purpose is.

It is for the fuel injector return.

The fuel injectors dont inject all the fuel delivered to them.  The excess runs out that line on the back of the head and adjoins the VP overflow outlet line at the tee fitting, where it all runs back to the fuel tank.