I did that on a Valmet 12 gauge back about 30 years ago. IIRC I got the triggers from Dixie Gun works. I don't recall it being terribly difficult but like I said, that was thirty years ago. Recently I converted my Fausti 20 ga O&U with some triggers from my miscellaneous junk boxes. They took a bit of rigging but I'm happy with the result. I can live with a single trigger if the selector is on the top tang but those with the silly button in the trigger itself might just as well be non-selective.