You will need a retaining ring or mounting flange for the shutter(s). I bought a 203 without a flange or ring, and ended up buying a flange from SK Grimes (they didn't have a stock ring for that shutter).
I seem to remember that I had to open up the Copal #1 opening just a bit to fit the 203 flange. And the Copal #0 opening a bit to fit the 105mm Ektar with retaining ring. I used a Dremel with sanding drum= the amount was small in both cases. It doesn't have to be a super-precise press fit.
I ran a test of the 203 Ektar versus a Caltar-II multicoated 210mm (Rodenstock Sironar, I believe). The Ektar was a touch sharper; the Caltar maybe a touch more 'micro-cotrast.' I have stayed with the Ektar. Enjoy the Ektar(s) for a while before worrying about other lenses.