/\ Be careful with those Glortismn like assumptions because whilst these engines will run to 2500 RPM, they would have to have had certain high speed options fitted from the outset, and without them, the life expectancy will be drastically reduced.
These engines are most likely a Lister SL4 engine, it could also be SR4 (it is difficult to tell exactly from the data plate).
Apart from a closer inspection of the data plate, the shape of the cylinder barrel finning will confirm it. The SL has a fin profile which follows the shape of the cylinder bore, ie more rounded.
The SR will have a finer pitch and the when looking from above the outline of the finning will be square.
If it is an SL (most likely) before buying, confirm these engines are good runners, and nothing critical is missing, as there are a lot of unique parts in an SL, and even more so in a four cylinder version.
These 4 cylinder engines are rare, and were typically used on grain dryer and marine applications.
Here is a marine version:
https://www.ebay.co.uk/itm/Lister-SL4-20hp-4-cylinder-marine-diesel-engine-vintage-stationary-engine/333382378189Here is an instruction manual for a SR4 grain dryer:
https://www.ebay.co.uk/itm/Lister-Type-SR4-Air-Cooled-Diesel-Engine-Instructions-Parts-List-Book-1398-1068/202556892415If it is anything else other than a good runner walk away, otherwise you could be having open wallet surgery thereafter.
Someone on here did document the restoration of one of these engine some time ago, and when he did so, he was lucky, as Sleeman and Hawken were on the knockings of the last of specialist parts he required (I know as I researched it for him, as you will see from the forum thread), see here:
https://listerengine.com/smf/index.php?topic=6174.0