1. Below the transponder are control cables making that space unusable. The GTN-750 has a space right behind the display for their audio panel so it makes it real easy to mount. I could have also remote mounted a GTX-345R instead of the panel mount GTX-345. Too many things relying on the GTN-750 is probably not a good idea.
2. $75K includes parts and labor. GMA-35C audio panel, GTN-750 WAAS GPS/NAV/COMM, GNC-255a NAV/COMM, G500TXi, GEA-110 engine monitor with all available probes including carb ice (temp) sensor, synthetic vision option, G5 backup EFIS, new instrument panel, Flight Stream 510, all new circuit breakers relocated to easy to access panel location. I valued the S-Tec autopilot at $10K. The S-Tec system 50 is around $17K installed originally. I will be putting in a new GFC-500 autopilot as soon as they are STC’d. Which should be less than a year from now. The cost of that installed is around $13K. That would then bring the grand total to high 70’s.
If you would like to see the invoice for an actual break down I can post it.