Lots of interesting replies to my query, thanks all.
I went with the big drum system because Lister seemed to have recommended it.
However I do see that over-cooling is a possible unwanted effect.
Anti-freeze I discovered was going to be expensive, but the engine is in a shed, though not an insulated one.
We get a few sub-zero Celsius days each Winter. Is it risky to not use anti-freeze in these circumstances?
I thought to avoid a thermostat to keep it simple. That has appeal.
I regret not using a radiator, I think. I do have one that could be appropriate.
It came from a very old big air compressor, so it cooled air. It has copper tubes with spiky, porcupine-like cooling fins on them.
I think it would do for the Lister, and looks interesting.
For the time being though, I will use the existing drum that I went to some trouble to install.
I'm thinking that temperature could be controlled by throttling the flow at the tank's gate valve.
Water at the bottom of the tank might be too cool, but restricted flow should bring the temperature to a happier level within the engine.
Temp gauge at the top to monitor.
Am I correct in this, or is there something wrong - maybe difficult to maintain a steady temperature?
At this stage I am always with the Lister when it's running, but in future it might be providing back up electric power and need to run unattended for lengthy periods.