'86 Trooper2 engine confusion

I picked up Trooper 4dr, 4wd at acution for $35. They pushed it through the bay and i figured if i couldn't get it to run I could always sell it for parts. Well I pumped the gas and turned the key and it started right up! It needed a break master cylinder that I paid $30 for and had it on in an hour. Great deal huh?
Well thats not really an issue,but I like to tell people about my great deal.
My confusion started today when i was giving it a tune up. I bought a new distributor cap and after stuggling to remove the old one I discovered the new one is atached by clips instead of screws like my old one. The parts store double checked the code and it was correct and my Hanyes manual shows a different cap then mine. After removing the air cleaner, on top of the motor i found "sold" which tells me that motors been replaced. So I have no clue what motor I've got.
My valve cover is smooth and says Isuzu right next to the oil cap. The book shows a valve cover with ridges on it. I also have a o2 sensor on my exhaust manifold thats not connected to anything and I can not find a wire where it should connect. Its a gas motor and carburated. I'm pretty certain its a 2.3L. But I thought it might be from a newer model because of the o2 sensor.
If anybody can tell me what motor this is, where a motor code might be located or if I am wrong and this is the correct motor, I will apprectiate any response. Thank You.

Seems to me they put an Isuzu engine with a smooth valve cover in some of the Chevy Luvs. This is just a wild guess. The valve covers on both the 2.3L engines I've had are not smooth. The O2 sensor started with the 2.6L engine, I believe.