Engine rebuild

I am doing a engine rebuild on a 2002 isuzu trooper and the tech manual instructs to remove the transmision first? I did a tranny bob on a rodeo and that was not fun! Is there any reason the tranny has to come out to pull the engine on this trooper?? also will a 3.2 L fit in the place of this 3.5L which is notorius for throwing the rods