whats inside your devere mk1 light mixing box

Hi

I have been cleaning my mk1 dicromat head and wonder if my light mixing box has been modified
it is lined with about 1/2" poly at the top which has melted a bit and gone yellow
then there is a prism sheet half way down
then there are strips of mirror with a square of white perspex set at an angle so it dose not cover the corners then more mirror and the end sheet of perspex

is this how they are supposed to be

thanks

robin