One idea I had was an electric transmission- a front mounted 3.5 KW petrol engine/generator with a 210 cc engine, and then the motor controller and motor from an old running machine at the back driving the rear wheels. I bought a running machine for a fiver and then converted it (with an angle grinder and a load of welding) into a bench and motor/speed controller for my 3.5” lathe; works really well. there’s loads of them on eBay.
Whitham Specialist Vehicles has had loads of ex government generator sets going quite cheap on their website recently, in amongst the Snatch landrovers and FV432s. This added to my Christie style rear suspension idea and.. errrr……well.. it’s a tank, isn’t it?