I got mine here, they are great quality. Its a OBO sale, I offered $175 and got them for $200, that's for a full set shipped.
This pic was taken from the parts manual.
The lift pump is a Bosch 'KE' type. For a 4BD1T the Isuzu part number is 894131-0130, but there are a few different versions for the early 4BD1, depending on the original application, many used Isuzu part number 894132-7040.
Have you checked the strainer in the inlet banjo bolt?
I had a look through my parts book to see if the later 4BD1's might have been upgraded with piston cooling jets. They do not.
If you happen to find that your late 4BD1 block is machined to accept piston cooling jets, the part numbers for jets used with the post 88, 4BD1T are:
Check valve 1131610120 (attaches the jet to the block and opens under pressure)
The part numbers I have for the post 88, 4BD1T are:
Dip stick 8943262030