how big is your Garmin? i use the Garmin Nuvi and it fits in front of the radio display, (also do not have MFT/Nav in mine) Sure i block the radio but i just put it on the Sat radio and keep it on country for road trips so i dont really worry about changing channels :)
Oh to put it in that space you do need to take off the mounting bracket. It should just slide it. slight angle so you dont hit the power button.