On my truck it runs behind the head, but I cannot get my hand back there to feel what it attaches to, but it would about have to attach to the head or block. Either one would ground the engine.

 

Any bolt on the engine that it will reach will be fine.

 

Straight down, attach it to that big stud sticking out and with the RFI capacitor. The 4sixes attached to the front of the engine, 5fours were shorter and attached to the intake. It's a very much needed cab/engine ground since the below the truck will rot completely away and break off. Need those grounds, otherwise, you'll end up with severe electrolysis issues among other goofy problems.

 

This is exactly what I would do as well.