1995 Nissan Serena Timing chain access?

Our serena is idling very strange, its almost sounds like its reving up and down on its own. Its been in the garage for 3 weeks they changed the cat and exhaust but this hasn't resolved the issue and now they believe the timing chain may have slipped which is causing the problem.
They have said in order to resolve the issue they think they will need to remove the engine to gain access is this correct?

its a 2L petrol 126hp model.

thank you