Keeping it 4WD, as a 2WD FL1 is pointless.
A Nissan Leaf motor/inverter can be coupled to the standard manual gearbox, in place of the engine. The gearbox could be used as a ratio change box for off road use, or simply left in 3rd or 4th all the time.
The motor has more than enough torque to accelerate a FL1 weight vehicle in 4th, and a high enough RPM range to make gear changing unnecessary. Reverse gear isn't needed at all, as the motor reverses direction for the vehicle to go backwards, which is something an IC engine can't do.
Brake vacuum comes from an electrical vacuum pump off another vehicle, as does an electric power steering pump. There's even an electric driven AC compressor available from another vehicle.
The standard FL1 PTC heater can be used to warm the cabin when cold, and the motor/inverter coolant circuit can be used to warm the heater matrix just like a conventional IC engine does.
An additional small radiator can be used to cool the motor/inverter when additional heating isn't needed in the cabin.
If the fuel tank is removed, there's a decent amount of space for a sizable battery pack, right there ready for use. There's also more space behind the rear sub-frame (where the rear silencer resides normally) and if the rear cubby box is removed (making the boot floor flat) then the space under the boot floor is huge. I've worked out I can fit over 30 kWh of batteries in those 2 locations alone.
The Nissan Leaf motor/inverter unit is much smaller than the IC engine, so there's more battery space up the front too, and even more space under the floors between the sills and chassis rails, if some ingenuity is used to assemble odd shaped battery packs. I think there's another 20 kWh or more of battery space under the floor, which would add to the range and usefulness of the vehicle.
The wiring integration with the vehicle CAN-BUS will be the difficult bit, but I don't think it's impossible to solve these days, as there are CAN-BUS emulators and converters available now. Actually getting the vehicle to move under battery power isn't that difficult, as there's a growing community of people developing motor drive controllers for the Nissan Leaf motor/inverter for this very purpose.
Thankfully I'm suitably skilled to do the engineering, but my stumbling block is the finances, which would be a considerable up front outlay, with no return until it's on the road. Also a suitable (immaculate) FL1 needs to be found at a good price, as there's no point in messing with a tatty or rusty vehicle to start with.
