Y07,
I used them on some MP cast aluminum valve covers on my 340 stroker. The spacers followed the contours of the valve covers pretty well.
At first, I tried sandwiching them between two valve cover gaskets, but ended up RTV'ing them to the valve covers. That way the spacers didn't move around between the two gaskets.
I'm no longer using them (changed heads), so PM me if you're interested.