The "analog" type heater controls are much bulkier than the "digital" type controls of the 1996+ M3's. If you've taken the glove box off, I think you will see the controls intimately connected to the vent system, which would make the movement of the controls hard.
I at one time thought about retrofitting my (1995) heater controls to the 1996+ digital unit because it is smaller, but many from the various lists (E36M3, UUCDigest, Bimmerforums, DTMPower) said it was difficult if not impossible.
If you are up to the task, you can get a relatively cheap used digital unit from
http://www.bimmerworld.com
Good luck!!
Wes
E36 M3