All cams require a specific valve spring installed height, open and closed pressure specific for the cams lift. A Z28 valve spring is only for use with a Z28 camshaft which is solid lift, and requires more pressure than any hydraulic camshaft will ever need, so you need to use the correct valve spring for the cam you are using or you can wipe a lobe off of the cam.
A stock SBC valve is shorter than a stock Chevy 6 valve, so I would use a .100 longer SBC like Hank said.
