Last year I updated 2919T with Garmin 530WAAS, 2x G5s, 330ES, and 255 NAV/COM. I was able to purchase refurbished 330 and 530, new G5s and 255. All of these worked well with my older Garmin Audio panel. With this install, you are able to remove the air pump and pneumatic gyros since the dual G5s have batteries and provide back-up capability (although I left my gyro in as a back-up until the pump fails giving me option to keep HSI if one G5 fails). I also kept my KI-109 to interface with the 255.
The install cost was as much as the component prices, given the number of hours involved. The Garmin data base subscription is reasonable given the capability provided. Total cost was <$30K.
I can send pictures of the completed install if you are interested.