It's a pretty old vehicle, and API CC is "Caution - not recommended for passenger vehicle diesel engines built after 1990"... so it would seem to match. There are still some fairly primitive oil types knocking around which seem to better suit the characteristics of older engines for various reasons. Never mind what the previous owner might have thought for his own reasons, right or wrong ... check the manual, see what weight or weight-range of oil it suggests for your climate, and see about getting hold of something that at least has ratings that intersect with the manufacturer's guidance.
Synthetic is generally better for highly-strung, hard revving, tight tolerance machines, like sportscars, motorcycles, and more modern, low capacity, hard blown turbodiesels with a focus on extremely low friction everywhere. I have a feeling that a lazy-revving 1980s utility-spec diesel that makes barely more than 25hp/litre (you can buy 1.4L TDis now that have higher output than your 4.0L) absolutely does not qualify in any of those categories, and would be perfectly happy, if not happier, with entirely generic semi-synth, or even "classic" fully-mineral not-at-all-synthetic still-has-chunks-of-rock-in-it super crude el cheaparino oil.
(For reference, it's also the oil recommended for classic put-put diesels powering canal barges or simple pieces of static machinery... which the 2H likely has more in common with than a 21st century engine making north of 60hp/L and liable to explode if it isn't run on space age 0w50 PTFE-doped super-oil that costs $50+ a fill... NB this isn't me trying to be down on the engine at all; it's obviously built to last, happily trucking along after 32 years, and will probably still be in fine shape long after all those little turbos have been scrapped, and the only way to run it is by putting chemically abused butter in the tank because liquid fuel filling stations are naught but a memory)