Thanks again 34_40! I've been reading about the checker springs. I suppose it would work as long as the springs in the lifers can overcome the checker spring tension, which I doubt to be honest. That said, I've never tried them.

I am rebuilding the engine stock, we're enthusiasts of American cars, stock performance is fine. I have a Comp Camps push rod checker tool, so measuring the correct size I can do, I'm just wondering on how to perform an accurate measurement when the lifters are throwing it off.

The springs are the double ones, stock ones. Are you saying that I should not try to measure it? It sounds logical to me that the valve guides will wear out more easily when I get it off. I can't imagine there is no accurate way to measure it... How do you do it?