I ran a set on my 440 for years.They had 2.14 and 1.81 stainless valves.That and I had new guides etc done plus they were opened up.Never had them flowed but they ran great.Now they are on my kids 413 and still going strong.They droped his ET about .3 over his stock heads.This was before aluminum heads were avaliable reasonable.Never had problems with the seats.He puts a ton of miles on the car every year.Now for a race only motor Id go aftermarket.Rocky