wasnt sure which forum to post this in, tpi, or tech, so here is the link , if anyone has the time to check it out, and advice , thanks in advance , http://www.thirdgen.org/techbb2/show...98#post1237398

The springs are only one reason the L-98 heads can't go over .470. The bottom of the retainer hits the top of the valve guide seal. Stock springs will actually go beyond .500" of lift without binding (I'm measured them in a valvespring vice) but they don't stand a prayer of controlling the valve motion with an aftermarket cam in that lift range.

You need springs AND machine work the whittle the guides down a bit.