There were two or maybe three variations in 1986 alone. I've bought and resold a few '86 power steering pumps. I can't recall how they differed -- whether it was the mounting brackets, pulleys, or hydraulic lines. One buyer returned a pump that "didn't fit" and I sent him a different one that did.
I imagine the 1987 variant should be like at least one of the 1986 pumps. And I suspect any of them should work, but may require some fabrication.
Jack
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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.comIsuzuPup.com