Hi Wayne,
Your engine was built on a rebuild programme at 44 District Workshop REME, Ashford, Kent. Sadly, no longer there, as the High Speed railway to Paris cuts across the site now.
I think the number stamped vertically is possible the last two groups of the NSN for this unit, when I was building engines on the line there, some years earlier, we did not stamp this in, but with so many variants of these engines, it may have been done for ease of identity.
If you found the word "Preserved" painted on the engine, this was done after testing and prior to packing, means it was sprayed inside with preservative then sealed up.
regards, Richard
The "S" stamps mean it has Standard size crank journals, ie Mains and Big end, probably a new crank was fitted.