Valve Cover spacers

Looking for some guidance here. I want to run fabricated valve covers on my 408 stroker with Victor 340 intake manifold. I know the valve covers will not clear the intake and rather than notching the valve covers, I would prefer to run a valve cover spacer. My question is, what is the minimum height spacer I need to clear the Victor 340?

Thanks in advance,
Bill

If your valve covers hit the intake manifold your manifold isn’t fitted correctly.