The cylinder heads control the power out put on all motors. On the 5.5 the gains were significant on the intake side this combination gives you 600 RWH. the work consist of

tear down and inspection debur and wash heads conture and polish ports three angel valve job lap gasket surfaces clean and assemble heads with new valve seals. the job also comes with a before and after flow graf to see what gains you are paying for. If you have any questions contact me and i will answer them