07 peterbilt 386.

Looking at a 386, guy told me it needs a new head. It has a C13 cat in it, and oil pressure is dropping after it runs a few minutes. Can a head cause this? Or would it be the cam screwed up the head?
Being I know nothing about a C13. I'm lost on this one for sure. Had a guy tell me to just buy the truck. Then swap out the cat for a ISX? Can it be that easy to swap in a ISX for the cat? I know it came with both. so guessing if I had the wiring harness from the 386 and then the ISX may be a easy swap.
Also Truck has 800,000 miles on it. And from the pics is still in great shape.
Pete

 

The wait time would be no issue. Found a motor and trans, at a steal. Papers on the in-frame last year. Truck was ran 65000 miles, then caught on fire. Burned the cab, engine was ok. Would love to try this build. Also found a place that makes the wiring harness for the swap. But feel the guy is just asking more then the 386 is worth. If it did not have the C13 in it. I would have had it home 3 weeks ago. AS if it had the ISX I would just do a in-frame on it. And run it until I'm done with it.
Keep looking for a 384 small sleeper and small engine. That way the weight is low on the truck. May even just single it out now. As in 2 years what every I get will be singled out. Then used to pull a RV for a while. Will be hauling almost a empty trailer with what ever I get. As load will only weigh around 5000 lbs.
Pete