Steven a quick update on your transponder saga.
I looked at the wiring diagrams for the KT-78 vs. the KT-76A (which I have 3 of) the wiring is different in three areas, so the 7i6A is not a drop in replacement.
So nothing I have will work without a rewrire. You are basically 24 months out of the ADS-B requirement so possibly put money in that direction.