As an aside, I just noticed a complete 3.0 diesel with automatic on eBay (item 300114703518). It's from a private seller who seems to know something about the automatic transmissions. Might be worth contacting him?

Note that this is the 3.0 common-rail DOHC diesel, not the 3.1 you've been discussing, but the transmission information may be applicable.

1988 Isuzu Trooper LS
2.8l Isuzu 4JB1-TC intercooled turbo diesel
www.dieseltrooper.blogspot.com