Now that the diplexer is on hand and schedules are coordinated with Dean we hooked everything up and attempted to install the Avidyne IFD540. But it wouldn't seat properly. Note the gap in photo 6365. After a lot of attempts and thinking everything thru we determined that on the first attempt we didn't drill the mount holes in the appropriate location - that is, based on the original cover plate. With the new cover plate in hand we then measured a few more times before drilling the new holes - and then went for it. This time everything went well and the unit fits properly and is finally installed as in photo 6367.