It's a drop-in replacement, I recently did it on my plane. Only thing you might need to watch out for is verifying that the serial port settings are the same on both units so the 496 will continue driving the TruTrack. This is exactly the setup I have.
You don't really gain a lot from doing this, as far as I can tell. I'm now in the process of replacing the 496 with an Aera 660. Wish I had skipped the 496 & gone straight to the 660.
I do have a 296 for sale, and will soon be selling the 496.