There's a guy on the IsuzuPup.com forum who has an S10 that he put a P'up diesel into. He found a Buick driveshaft that fit the output shaft of the P'up transmission, and bolted right up to the S10 rear end. I'm not sure if he has a short or long bed, but I'll see if I can find that post and link it here.
Update: It's in our "Parts" section, which isn't "public". So here's the quote:
Youngcummins wrote:
ok well it turns out that a drive shaft out of a 79 buick regal with a th350 fit PERFECT!!
He has a regular cab, long bed S10. My guess is you'd have to have the driveshaft shortened, but that wouldn't be hard.
Jack
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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.comIsuzuPup.com