440 source sleath heads

I have a pair in a box, been sitting new for 3 years.
I called them up the other day about changing spring hardware and he said, "if you are running .550 - .575 lift, just bolt them on". If you are going more radical, change the keepers and retainers. The springs were, at time of purchase, rated for .600 lift.

Lots of folks recommend having them sonically checked prior to running.