Slide-in Garmin GTX-320A

The KT-76A finally went tango uniform so I'm getting a Garmin GTX-320A with
the adapter for the King transponder. Actually, the KT-76A still works but
it takes 45 minutes to an hour for it to warm up so it's equivalent to dead.

Has anyone out there gone the slide-in replacement route on the Garmin? How
was the experience and did you have to get a new antenna (I have the
pole-type)? Lastly, was it a logbook entry or did you have to get an
avionics shop so do anything else besides the IFR transponder check? The W&B
seems to be negligible given the 1lb weight difference.

Thanks in advance.

Marco