I did this mod about a year ago but have since gone back to the original screen. The focus with my split screen was slightly off. Probably the side pieces I glued on weren't exactly thick enough. The green dot works better for a variety of lenses. Especially with slower lenses the screen is a bit too dark. If I'm really itching for split screen I can break out my Nikon F2 with a roll of Tri-X in it.There appears to be a Nikon option.
https://richardhaw.com/2016/09/11/mod-nikon-df-split-prism/
https://ebay.com/itm/396074903914