Bruce,
I am finishing up the upgrade for my 680FL, three weeks only turned into a couple of months. It is a combination of old and new.
I kept the Garmin 530W, added the Aspen 1000 Pro with AOA, added L3 NGT9000 and Stormscope, and had the Bendix M-4C box and all servos overhauled by a retired Bendix guru. There really wasn't an alternative on the autopilot. I also moved the engine gauges to the top panel and installed a JPI 760 and Shadin Fuel Flow gauge. The electrical system was completely inspected and re-wired as needed. I panel mounted the Garmin 696 that I already had. I fly with ForeFlight on my iPad.
I am to get the bird back on Wednesday. In reaching the combo of old and new, I gave some consideration to the panel in the Cessna T-210 I also have. I previously went with a Garmin 345 in it and it has performed admirably, with Garmin 430W installed.
Here are a couple of quick photos taken. Not the best quality but you will get the idea.
Brent
1966 680FL
N742W