I bit the bullet and got a GTX345.  Shop called back and said my avionics stacks is riveted in and replacing the transponder just went from 15 to 30 hours labor.  They said they have no problem with owner assist.  Theyll give me the tray and i can install it. My transponder is above my INOP ADF.  Any body got any tips on removing the AT50A TSO tray?  what else has to come out to get to what I need to get to.  Are airplane rivets the same as any other rivet and I just have to drill them