Greg, nice to hear that you want to preserve these guns and shoot them. The only one that would have short chambers would be the No. 2 16 gauge. They would at this time be 2 9/16" and if it was mine I would not change the chamber length. If you just want to use it for some preserve shooting you will not be shooting that many 2 1/2" shells so I would just use RST's. There are some on this site that do have their 16 and 20 gauge guns chambers enlarged but I personally don't like that idea because you are going into the forcing cone and the barrels wall thickness is now compromised.
As to a gunsmith I would only bring them to one that knows L.C. Smiths and is recommended, there are many out there that say they are familiar with them but they are not. I'm sure you will get some answers here.