Customer dropped off a 472 Crate Hemi--tag says Cummins last digits are 666 AC--it is several years old been sitting since bought--what are the things if any that need a look on this before install--I know the older units had problems -crate says dyno but looks like a few minutes on a test stand to me--pulled intake and covers--pushrods all have room--cam and lifters look like they have run some and look great! Retainers look wimpy and do not fit the single spring--does it need a different spring and retainer--single seems like borderline on this to me--Thanks for the help!