If it has worked for 75-100 years so far you should be all right. If in doubt send it out for an evaluation by one of the gun smiths mentioned here to have them look at the trigger and make sure it has not been fixed by some semi literate fool.

You are looking for a field gun not a clays gun. The difference is about 10-20 times more shells shot in a clays gun per year than a field gun. If you were gong to shoot ten grand of shells a year I would pass on the single trigger on any English double.