Going by pictures in Mark Hayward's "Sherman Firefly" book, it looks like some did have a single smoke emitter on the lower right rear plate and some didn't. In the book there is a drawing from the Tank Museum and it shows two smoke dischargers on the side of the turret. So that may be the reason some had it and some didn't ? They didn't use the lorry like spring mount for the tow pintle on the 1c. I believe it would have interfered with the exhaust deflection louver swinging up and down if mounted.
I have indeed found a number of photos on the spring towing pintle, or its mounting brackets, mounted on Ic and Ic hybrids. Rear smoke dischargers can be seen too. Two books look into this tank in detail. Both have the same title; Sherman IC Firefly, both are written by Wojciech J Gawrych. But they are two different books the first published by RossaGraph in 2004, the other is the recent Armour photoGallery #21 by Model Centrum. Lots of photos of Polish Ic inside both books. It seems that the mounting is more or less identical to the one on Sherman V and Vc, both versins having twin doors on the rear plate. Your best way to replicate it is to look closely at the Tasca Sherman V or Vc. BTW, I have read that Dragons model of the Sherman Ic hybrid does have it too. Mounting brackets and smoke dischargers can be found in ABERs basic set for Tasca's Firefly Vc. IMHO there would have been space enough left for the exhaust deflection louver louver too even if it would have been cramped. I haven't seen any photo of that combination mounted simultaneously, but at least one photo of the exhaust deflector and mounting brackets can clearly be seen (Coldstream Guards w/ Typhoon rockets, outside Bremen April 1945. IWM BU3584)