That piece actually IS the bearing. One of two actually. It's a piece of metal with three babbit bearings on one side, and a flat backing steel on the other. The whole thing should sit in a shaped notch on one side of a crank main support (block side, not main cap).
Actually Isuzu calls them "Thrust Washer". You can see it if you go to myisuzuparts.com and select your year and trooper, then in the middle pane select "Parts Catalog", under that select "Engine", then in the right pane select "Crankshaft, Piston, and Flywheel", and finally select "4ZE1 Gasoline Eng" in the bottom left and submit at the bottom. It's labeled part #42. Sorry if you're familiar with myisuzuparts but I couldn't find a way to link to what I was looking at.
I would ask others that have that motor and I hate to be the bearer of bad news, but I think and engine pull and bearing inspection is going to be in the future.