For the split image you can go for the Rick Oleson's bright screen MPD type, I have myself a MP for focusing and it does very well. If I remember correctly you need to the metal frame of your current screen and install Rick's.
For original Kowa screens I only saw myself the microspot II.
Thanks for your reply. I know replacing the focusing screen is a simple process. I will look into the Rick Oleson MPD screen and hopefully with some luck find on that will fit my ‘78 model 6 Kowa.