I had an old Ford slant six in Boracay, but it was in very poor condition and major spare parts
were like hens teeth so I ditched it and put in a John Deere 4045 DFM, and very glad I am that I did.
Please note that rebuilding an old engine
is very expensive and repowering should be considered.
If your engine/gearbox is basically sound then "usual" spare parts
may sometimes be found at truck spare parts places. It's a may be good idea to get friendly with their part "guru".
For less common spare parts you may care to start tapping into the ether, as some of these are an "enthusiasts" engine
I'd recommend that you find out exactly which engine you have, and who it was marinised by. I'm guessing it is either the Ford Dover or Ford Dorset, but, to emphasise, it's only a guess. If I was betting I'd put my money
on a Lees conversion.
I found the following links with a quick search. As you find out more about your engine the parts situation may become clearer.
Dover or Dorset manuals?
Identifying the Dover or Dorset
Same engine as Lehman?
Discussion forum on old diesels