The diesel will not bolt to the V6 bellhousing (or the 4-cylinder bellhousing, for that matter). It requires, for all intents and purposes, its own specific transmission as the bellhousing is part of the transmission case.

You would need to obtain the complete diesel engine/transmission from a donor diesel Trooper.

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