I don't have a direct answer to your question. You might ask around if there is a CONVERSION BARREL available for the IMI-made gun. If not, the barrel diameters might be different.
That said, I've known people to shoot 9mm Glock barrels (which don't have the same diameter as the .40 models) in a .40 slide and get pretty good results. It may depend on how well a particular barrel locks up in a given slide and frame.
The Witness models (based on the smaller frame size -- like the 75/75B -- no longer used in Witnesses) were originally based on the same (licensed) Tanfoglio version of the CZ pattern, the 9mm and .40 barrels eventually were produced with the same diameter and you could generally just swap barrels. I don't know if that's true of IMI guns.
With the Witness guns you didn't always have to swap magazines, unless --and only in some cases -- you were shooting hollow point ammo. (The big mouth on some 9mm hollow point ammo would bite into the feed ramp when using the .40 magazines.
(I have used conversion barrels in some of my .40s over the years, and they often work well when using 9mm ammo in a .40 magazine -- unless you're using SOME BRANDS of hollow point ammo.)
