[HO455]

Maybe someone could help me as I don't have much of a pattern left. (See photo before it fell apart during disassembly) In regards to the "Key" piece that goes in the front passenger side corner. From what I have been able to learn from some of Vectorit's posts (Thank you sir!) is the piece has a tongue or groove that has a mate on the main piece. It makes sense to me for the groove to be on the main piece and the tongue on the "Key" piece. If this is true then how long is the groove on the main piece? Do I need to make it twice as long as the "Key" piece or is there enough wiggle room to only have as much groove as the"Key" needs?

And the second inquiry is about the blue sheet metal piece in the photo is there suppost to be a corresponding piece on the driver's side too?
Thank you in advance.