Dom,

That 590 cam might be just big enough to be a torque killer on Ron's son's 406. With his combo and weight the 557 seems to be to be just about right and it works very well for what is essentially a solid running and reliablly consistent package. 383-400's are more cam sensitive than any other motors in our stable due to that long rod short stroke. If I were to do anything on a 406 like that I'd run the longer 6.76 LY rod to get the piston weight down and lighten up the bob...that would work the heads even harder up top with no real downside.