Bronco II Negative Battery Cable

Generally attaches to frame

How important is it that it be bolted to the frame as well as the engine block (no suitable place within reach to bolt to)?
If not important, should I tape off, or wrap, the brass lug?

It's important to have SOMETHING between the battery negative post and the body. It doesn't matter if that is the connection in your new cable or an existing ground strap between the engine and body. Your new cable is the path for the starter's current to the engine and some of the electronics on it. The entire drive train is insulated from the body because it is mounted on rubber engine mounts. There has to be a return path to the battery for the brake lights, head lights, radio, and other stuff in the vehicle. If everything works fine with your new cable, there is already a ground wire to the body somewhere. Bolting that connector on your new cable to the frame or body won't hurt now but it will prevent any future problem if that existing ground strap corrodes off. If the vehicle is dead when you turn on the ignition switch or any other electrical things, then you need to bolt that connection to the frame or body.

Thank you so much for the information. I could not find a suitable place to bolt the intermediate lug to the frame as there is not enough overall length to go from the engine block to the battery terminal and an available frame hole in between. what I did do is attach the lug to a stud bolt on the exhaust manifold heat shield to keep it out of the way. I am not sure this is a good place due to the heat though.
there are 2 other leads that come off the main terminal clamp. One is a ground wire that attaches to the body next to the radiator and the other looks similar to an in-line fuse but is not and makes a connection into a large wire loom.
I believe I am grounded well enough but not sure if I should remove the lug from the exhaust manifold heat shield.

Sounds like that lug is meant for some other application, ( can be used on a different vehicle). That small wire you found that attaches to the body by the radiator is the important one for the rest of the electrical system. Bolting that lug to the exhaust won't accomplish anything because the end of the cable is bolted to the engine. Electrically-speaking those are both the same point. I think I would remove it so the heat won't degrade the wires.

Thanks for your help.