Steamtrainfiend

I was recently given a tender driven plastic bodied Britannia. This being my first conversion I have been on a learning curve. I have been told that the following should fit. Zimo MX645R dcc and sound chip PowerCube9 speaker SuperCap17000uF Stay alive. I have yet to pull the body apart. Before I do I was wondering if anyone has done this conversion before, how much space is inside the boiler, how big is the weight inside the boiler and if the above parts will fit. Any pics greatly appreciated. Thanks in advance. James