I have just finished and commissioned the full conversion to SVO on Reggie (1990 Defender 110 200Tdi).
Total cost was around £230, I hope to get the cost back in 6 months or so.
I bought a heat exchanger (with hot water pipes) (£65) and Pollak valve (£46) from Biotuning. My first Pollak valve (from an American seller on ebay) turned out to be a dud and lasted all of three operations!
I had a separate aluminium fuel tank made (approximately £80) to my dimensions to fit a specific space envelope.
Fuel pipe and "proper" pipe clips were bought from a UK ebay seller.
The control system comprises a 60 degC thermal switch (RS), two relays (Rapid Electronics) a toggle switch and a buzzer. There is a bi-colour LED mounted in the dash between the fuel gauge and temperature gauge.
The heater is fitted in series with the car heater circuit. The thermal switch is mounted on the top of the heater using a tie-wrap and conductivity is helped by thermal paste. The whole assembly is mounted under the top of the front wing, insulated from the aluminium by a couple of pieces of wood.
The Pollak valve (only takes power to move and is un-powered at all other times) is fitted next to the clutch master cylinder. A second fuel filter is mounted on the front bulkhead.
The control system is complicated than it could be, but as my wife sometimes drives Reggie I wanted it to be fool proof (I would say idiot proof - but she may read this :-)
With the ignition off the LED is red (this is driven off a contact on the valve, so shows me the true valve position). The toggle switch is down and the buzzer is silent. On starting the car the LED will stay red until the heat exchanger external surface gets to approximately 60 degC at which point it turns green indicating that the switch has been made to SVO.
Approximately 2 minutes (or a mile of so) before the end of the journey, the driver operates the toggle switch and the LED goes red indicating that we're back to dino fuel and purging the system. When the engine is turned off (and if the toggle switch is still in the "purge" position) a buzzer will sound, reminding you to put the toggle switch back down, at which point the buzzer will silence.
As we progress into winter I will see if the SVO is staying warm enough with just the heater and whether or not I need to insulate any of the pipe runs.
Cheers
Peter