All the larger SMX heads had cooling fans (350/400/600 etc). The AH250 SMX models (later called 280/300) originally had heat sinks fitted but then TE started fitting fans instead.
As has been mentioned, TE did seemingly chop and change and use whatever was available to them. I've had several 250 SMX heads appearing to be from the same era (i.e. the continuous line around the fascia) and some had heatsinks and some had fans. I prefer the heatsink purely as that's the type I had first and fell in love with. 😍