That is the plate under the rocker cover where the lifters sit and the rocker shafts and arms bolt through on the head. There will be 2 of them. Not sure of the 'factory' name, but I would call it a lifter guide plate.
Why do you need a replacement ? Is yours worn or cracked ?
yeh that's them, I soaked mine in some degreaser was way harsher than I thought now its gone all messed up don't know how to fix it any ideas or should I just buy a new one ?