I suspect that Ill have little weight left for armour .....maybe 1.5 - 2kgs.

Approx 1kg each for the battery and ram.

The battery will slide up inside the middle leg of the T formed by the Ali channel main chassis.....The ram will angle back towards the 3 port F.P. Valve , between and following the line of the flipper legs.
The speed control , switch etc lives inside the rear channel.