My 3.8 locked up a few weeks ago with 190k miles on it. I don't know the reason for locking up but figure for the time and money to rebuild that motor I'd be further ahead to replace with less miles. I'd like to put a 4.2 in it, no replacement for displacement. I understand this has been done several times with a truck motor. What about a 4.2 from a van? I can find those with low miles all day. Truck motor not so much. I know ill have to swap the intake and fuel setup over but is there any real difference in block and heads between them?