There are two different sized copal 3's

I have a newer (serial #83XXXXX) 24" Red Dot in a new Copal three, and it works great. Mine has the elements on both sides of the shutter

I also have a "4 Ilex shutter and it would never fit my 24'

Talk to the people who mount lenses in shutters for a living, and they will tell you what works, and how much it will cost to make it work.

I machined a shutter (Packard) box with a varible iris that holds all of my barrel lenses
or shuttered lenses that I want to test with out mounting on a lens board.