As a follow up: I finally got around to dealing with replacing the barrel on my Solothurn AT84S. I ordered a replacement CZ 75 barrel from CZUSA to try and fit in my pistol. It turned out that the barrel diameter and upper locking lugs were a perfect drop in fit into the slide. The only things that needed modification were the lower locking lugs and the underside of the chamber.
I had to take some material off the front of the lower lug where the recoil spring guide rod rests, to allow clearance for reassembly with my pistol's full length guide rod. I also had to file down the inside upper surface of the kidney shaped slot to allow the slide lock pin to fit properly. Lastly, and most time consumingly, I had to cut grooves into the edges on the underside of the chamber after I found that lugs or tabs on the inside of the slide were interfering with full travel of the slide and preventing lock back.
I did most of the work with a dremel. It probably would have been smarter (and cleaner looking) to have a machinist mill out most of the mods, but what fun would that have been? The end result isn't quite as pretty but locks up rock solid and seems to have full and proper function, so after I take it to the range and prove function I'll call it good.
