Funny....not that I'd recommend it, but I had Briley install thinwalls in a 16ga SxS about 6 years ago.
No matter who does it, a set of screw-ins will cost you more than you paid for the gun.
If I were in your position, I'd pursue jug choking first, especially if I were looking for < .010 max. For strictly WC/grouse you might want to leave the first Cyl and just work on the second. If I wanted more choke than that, I'd pursue soldered-in choke sleeves adjusted to pretty much anything I wanted. In any event, I'd get the barrels into Mike Orlen's hands and let him advise me which way to go.