Do some research on the amount of spring pressure you can run with the hyd roller lifters, and how high you can turn the motor with the combo. A good friend of mine put hyd roller lifters in his low deck 500" Procharger motor,and it dropped 2 valves on the first pass. He got conflicting info from the Comp cams guy and the Procharger guy when he was planning the motor, and almost junked a set of B1 heads because of it. I wish I remembered the exact details so it would be more help, but it's been several months since it happened. Find out as much as you can before you plunk your money down. Good luck.