I've read good results of new valve seats pressed in with more interference fit and a "peening" to retain the seats. The rockers falling out are mostly caused when a hydraulic lifter collapses and allows too much clearance. A newer than 2008 head has the front most rocker post casting supported by a web to the head so it cannot break off like early 2000's 4.7 heads. Beyond that the 4.7 heads are ok reliability wise. Unfortunately the 4.7 doesn't have the good breathing/flow of the 5.2/5.9 heads. The 4.7 power curve is simply lacking until 3000+ rpm. Unilike the power curve of the 5.2/5.9 which is fat and cresting from 2000 rpm up to 3300. The 4.7 ngets there at 3300, finally, and then drops off quickly.