rocker spacers.

well, with hydraulic lifters, you should have no "rattling" rockers at all. There should be some preload on every one. Preload is the small amount of compression the plunger of the lifter has, when the lifter is on the cam's base circle. Also, if you are pulling it apart to check the timing chain, invest in the video/kit "How to degree your cam". dot to dot is about as accurate as eyeballing a cylinder head to see it it's flat or warped. It's the best $50 you'll spend, just remmeber to buy one with a small degree wheel, so you can do it in the car..otherwise the wheel hits the K frame. It will surprise you how bad "dot to dot" is. Also sounds like you need to check lifter preload if you havent, and the engine was rebuilt with either the heads, or block were milled, or you swtiched head gaskets.