37901 later Europhoenix roof conversion. This consists of a single printed roof panel with all the detail incorporated. This later version has the single exhaust port. As fitted from the europhoenix conversion without the silencer. 
To fit the exhaust panel a large hole needs to be cut into the roof starting at the rib at the fan end of the loco to 1mm before the rib of the exhaust which has been removed from the model (see the last photo). The print is angled so it sits in the hole with the sides slightly beneath the side rib line.