The Lister engine uses a 55 gallon drum set up to thermo siphon. That means the water will circulate from the engine to the cooling tank and back to the engine again without a pump. The way it works is the water in the block of the engine gets hot. The hot water raises in the hose to the top of the cooling tank. This water is replaced by cool water from the bottom of the cooling tank. As long as the top hose remains below the water level it will continue to work, but as soon as the top hose is above the water level, the process will stop. This will also work with an automotive radiator.
The tricky part of building the tank is welding the hose fittings to the side of the tank. If you are a good welder, it is a simple process. If you aren't a good welder it is almost impossible to make a watertight weld. Most likely you will melt a big hole in the side of the drum or at best the weld will not be watertight and leak. Well, here is a real easy way to put a pipe fitting into a steel or plastic drum without welding.
Here is what you need.
2 galvanized floor flange fittings
4 Nuts, bolts and washers that fit the holes in the floor flanges.
1 A 1/8 to 1/4 inch piece of rubber gasket material.
1 drill and drill bit slightly smaller than the bolts.
A drill bit the size of the bolts.
NOTE: if you are using a steel drum or don't have one big enough, you can use the small drill and drill a bunch of connecting holes and knock out the piece.) wrenches to fit the nuts and bolts. Some sealant. Cut a hole in the gasket material top match the inner hole of the floor flange. Drill one bolt hole through the flange and gasket. Place the flange over the hole in the drum and drill through the hole in the flange and then through the drum. Place the second floor flange on the inside and snug up the bolts and nut. Drill the other three holes and insert the bolt as you drill each one so nothing moves. Next, disasemble it and use the flanges to drill the holes in the gasket. Usa a slightly smaller drill bit then the size fo the bolt. If you do it right, you won't need the sealant. Now reasemble everything. Here is what it looks like when you are done. I didn't trim the gasket so you could see it better, but you can trim it to make it look better.