Good idea and all correct comments above.
To lighten the airframe and reduce the complexity l would suggest the following...
1. Remove the the complete bleed-system from the frame.
2. Remove the APU (The one at the back!).
3. Remove all pressurisation related components.
4. Remove all ant-ice related components.
That should free up a couple of tonnes.
For crew cooling, just install a 115V domestic AC up the front somewhere, with an air scoop close by.
The engines are a worry, but if they reckon they are cheaper to maintain than the radials on the neptune then good luck to them, especially with twice as many.
halas
(Just a tought, that without the APU in the tail the CG would move in the correct direction. May become a little pitchy, but that would be a good thing for this role)