I am not sure of the answer to your engine to bellhousing question, but a couple of quick Google searches yielded the answer that the Toyota 3.4 is rated at 190 hp and the engine in your Rodeo is rated at 194, so that swap isn't going to be of any help to you.

All of the Isuzu's are really a lot heavier than they may look. I don't want to urinate on anyone's Wheaties, but any engine swap is going to involve a lot of work, some of it fairly involved.

You might want to look at an option that improves what you have. At one time, there was a company that was importing superchargers for the 3.2. Some time with a search engine may yield some answers for you.

I am assuming that you are talking about improved performance ON road rather than OFF road.