I know what you mean about never seeing them,but originally on the block ends only, that was the case. If you noticed there is much less block to cylinder wall clearance on the ends then the sides of the block. Maybe factory installers installed them dome out because of the minimal clearance.I don't really know,but having done 2 235's and recently a 216, the end plugs were dome out.Of course my 235's were 1955 vintage,so maybe the newer 235's have the end plug dome in.It probably doesn't really matter anyway as long as they are installed carefully and with no or minimal sealer.
