Yes its a year, would be a bit excessive for 6 months! 
Avoid the pre-Y reg HDi if you do go for a 306 imo...remember tax goes on the car rather the engine when you swap, even if you use a newer 206 engine.

Avoid the pre-Y reg HDi if you do go for a 306 imo...remember tax goes on the car rather the engine when you swap, even if you use a newer 206 engine.