Personally I would not go to the expense of unleaded seats unless they were seriously recessed and affecting performance, and I couldn't find another good head economically. When unleaded seat replacement first kicked off many years ago I had a cylinder head for a triumph bonneville done (along with new valves and guides) at great expense, wish I had not bothered after one of the seats fell out and wrecked the top end. And that was done by one of the well respected gurus at the time. I can still find old heads with excellent condition valve seats and look for those whenever I need one, as I can get one cheaper than having unleaded conversions. Also if I was getting unleaded seats I would just do the exhaust seats as the inlets run cooler with the intake of cool air / petrol mix. With unleaded fuel you might need to retard the ignition a degree or two if the engine pinks, modern unleaded seems to be a bit more volatile than the old four star.