1991 Sierra Rebuild Question.
 

I have a 1991 Sierra 5.7 350 4X4. The dealership said the valve seats were leaking oil in to the #1 plug. In this case they said i could rebuild it or put a crate motor in. What would be reccommended and is there a way to only fix the top head of the motor. The truck has 200000 miles on this motor and has never been rebuilt.
Thanks