If its of any help, this engine is nearly identical to the Lister Petter TS and TR range, the only differences being:
1), The TL series has a belt driven axial cooling fan, compared to the TR /TS engines which have a flywheel mounted fan.
2), A slightly different timing gear cover which allows for different mounting arrangements for auxiliary drives to such items as hydraulic pumps etc.
3), Different SAE bell housing, when compared to the TR/TS series.
As a bare engine they are otherwise identical.
Hence if you are unable to find a TL manual, the TR/TS manual will give you most if not all of the important information that you would normally expect to need.
FYI: The TL series was only made as a 2 or 3 cylinder version whilst the TS and TR series was available as 1, 2, or 3 cylinder versions.