Macca,
The weight of our Taipan 5.7 external 10:1 mainsheet system is 3.3 kg (excluding the mainsheet line itself).
This includes the aluminium boom + all 10:1 system mainsheet blocks (including centre-sheeting).
How much do you gain by changing to an internal system?
By the way, do you contruct your new super-Taipan boom from off-the shelf carbon tube?