Did you break the cam in properly? Flat tappets are pissy with oils these days.
As far as preload, minimum is best, 1/4 turn, but anywhere from 1/4-1 full turn is fine.
A lot of valvetrain noise is from rockers and cam. Which rockers are you using? Chances are the Edelbrock cam is just noisier than some, customs tend to be the quietest.
Who cares how much horsepower it has, all that matters is how fast it goes!
Untested 331, lots of suspension, chewing up corners.