Jap plate dimensions ?

[EJ9 D-man]

I have recently purchased my EJ9, i have started to colour code the black plastics and im now wanting to fill the rear recess with a square plate and remove the disgusting rectangle one, does anyone no of a good site where i can buy ones to fit or the exact dimensions i need ? would really apretiate the help as a lot of the plate creator site have baffled me slightly with dimensions. thanks Will.