Mancini has a 2 piece stainless plate available for a reasonable cost , it will work with either B or RB engines , you have to drill the holes in the center to seal it & at least you do not have to remove the head if it leaks or you need to get to the lifters for some reason , l am sure you could make one like it out of sheet metal easily though .
T&D or Jesel make some awesome stuff ,Cheap too !! ......................... Not
Neil, do you have a link to the plate you mentioned?