Hey GB, how is your fuel filter attached to the cylinder? I know on some, if you remove the 4 bolts that hold the filter back plate/mounting bracket to the engine, you will find a cavity behind that backplate. I think the original listers had an access port into the coolant cavity there, and you could see the cylinder liner with the plate removed, but the roids just usually have a sealed cavity behind the plate. I think it was Hotater that suggested possibly using that cavity as a fluid heater, possibly to help warm up circulated engine oil from the bottom of the sump(the lube oil takes a long time to warmup on a roid). It might also work to heat WVO up close to 200F/coolant temp.
His suggestion was to make up a custom plate with holes that match the 4 fuel filter mount holes at the 4 corners of the cavity. To this plate weld two NPT fittings with holes thru the plate into the cavity area, one at the top near one corner, and one at the bottom near the opposite corner. Then bolt this plate in place over that cylinder cavity using the 4 fuel filter bolt holes, with a gasket between plate and cylinder to seal the plate to the cylinder. You could then feed WVO into and out of this cavity to heat the oil as it passes near the thinner inner cylinder wall. You would of course need to do some modifications to the stock fuel filter to re-mount it, but it might be better to add an aftermarlet fuel filter anyway, something with locally available filter elements, especially if you are going to run WVO. An aftermarket fuel filter mount could easilly be incorporated into the new cover plate. At the fuel flows of these things, I think the fuel would have plenty of time in that cavity to reach coolant/cylinder temp. Then you wouldn't need as hefty a final heater to peak the temp prior to injection.
I also saw one of the universities using a brazed flat plate heat exchanger to use engine coolant heat to pre-heat their WVO. These flow well and can support thermosiphon as it is what I am using to reclaim my coolant heat. If you put it above your radiator(upper hose runs to top of heatex, lower port of heatex feeds into top of radiator), you would still be able to thermosiphon coolant thru it to your radiator. You would have to move your expansion tank line to the highest point at the top of the heatex, but it would work.
Ron