Big Oops... Had to move the instrument panel aft about 1" (2.54 cm) because the cabling for the Garmin stack extended beyond the back of the panel by about 2/3 of an inch (1.9 cm). Tonight I found out that the passenger control column hits the panel face before there is sufficient down elevator. May mean trimming off the top of both control columns & using different grips that do not extend above the top of the column. This may also cause sufficient delay as to prevent having the aircraft ready for Oshkosh :^(