I rebuilt the panel in my airplane about a year ago with many, many pictures of the process. Specific to radio trays, I found they had a to be mounted a little higher than what you can put on the panel because of the cross-member/stringer F-402C.
On my panel, I raised the bottom edge by 1.5" to accommodate knees and longer legs so if you're going by plans built dimensions, you'll have an extra 1.5" hanging off the bottom of the radios other than what I already have.
Thanks for the reply.Im looking for the layout of avionics tray to mount remote boxes for transponder ads b receiver ,as you know rv4s don?t have large panel are .iwant to mount as much as is able behind panel looking for photos of others solutions thanks Pat Cullen
Dad helped out and ended up making a shelf running along the longitudinal axis (if that makes sense...) My GRT MAP sensor box, ADS-B, and GRT ARINC429 box are mounted there.
Oh... and nevermind the melted uAvionixs Echo cover... the shop light got a bit too close.