[Lynn]

Don't know that it was a sudden change over. Late cars (08A and after) have been observed with the "new" base that is not completely flat on the bottom, but not every one of them. Kind of like the valve covers on Zs and L46 Corvettes. Some, but not all of the late cars got the valve covers with drippers. But... unlike most of the dripper covers, they still have the short cut outs for the intake manifold runners. During that period a car could have received either the old or the new style of either.