Hi Pete.
I may be completely wrong here, And I'm sure Myles will put me right if I am
But my understanding is that the pushrods need to be the correct length to allow the correct rocker contact with valve tip. This can alter if you have had, either the heads skimmed or the block decked. I see no need for adjustable pushrods, But only ones of the correct length.
http://www.trickflow.com/product/for...ushroddata.asp