I bought the F6-J Nikon focusing screen from focusingscreen. They are in Taiwan. They include the tool to take out the spring wire. That tool helps a lot. Very glad I had it. Don't want to risk a screw drive slipping off and scratching the mirror or something else. Also include shims to adjust focus as well as a quality tweezer and some other bits. Also like the fact that is a genuine Nikon focusing screen. Very happy with it.
The split prism drives me nuts, so instead went with their F6-J micro prism. Although is probably easier to focus with split prism than the micro prism. Have on order a DK-21M Magnifier for the view finder. Will see if that helps with manual focus.