It is noteworthy that this thread has drifted from nose heavy to tail heavy and back again. And all eminating from the same question of what would you fit on a standard EC135 airframe.
All the variety of answers has tended to queer the pitch for the standard question of 'How does type X fly?' ... and underlines that there is no real answer without first clarifying the specification, equipment fit, role and required mission. All tempered with compromise. Yes, fly two pilot but do not forget to slide a few kg of lead down the tail boom.
That neither the 'standard' Eurocopter police fit [everything up front on mounting beams] and the McAlpine role pod solution actually represent a finite answer to the tail heavy bare airframe is noteworthy. The best place for everything might be on a centre line beam... but wait on... here come lateral CoG to mess up the sums!
It all points to a need to be an expert in weight and balance design BEFORE you sign off the final payment!