The GAE 12 takes the place of a configuration module in GTX 335 or 345 series transponders. The GTX 327 does not have the ability to receive altitude information from this unit.
The GTX 327 can accept pressure altitude from a serial or grey code encoder.
You will see that an IFR navigator can provide the GDL-82 GPS position, and in fact, you can purchase the gdl-82 without the onboard GPS.
Page 4-3 describes how you can use a GTN 6XX/7XX or GNS 4XXW/5XXW.
Page 7-11 says you can select ads-b+ format 2 from a GTN navigator.
Page 53 of the GPS 175 install manual says you can define a serial port as ads-b+ format 2.
So, I suspect if you wire the TX of a RS-232 port on the GPS 175 to the RX of the single RS-232 port on the GDL-82 and select ads-b+ format, it will work.
According to Stein this will work using the GDL82 antenna for the 175 and the 175 RS232 for the gps position to the GDL82, saving one antenna. I was going this route but ended up putting in the 375 but did use the GDL82 antenna.
Figs