Do domed KYB 399’s interfere with 302 cast heads?

The 399 is a quench dome that's meant to be milled to achieve optimum quench in the heads they are used with. So no, AS IS, I would imagine the domes will hit the quench pad of the 302s. But the domes can be milled to make some really nice quench. Call United Engine and they can tell you more.