1999 Pontiac Grand Prix Pressure Build up

Hi, I just put a used motor in my grand prix. It came out of a 97. When I started it up it ran like crap, with smoke blowing everywhere and the check engine light flashing, There is a lot of pressure built up in it because when I take dipstick out I hear a high pitch wistle, and when I take the oil cap off it completly shuts off. I replaced the PCV valve and doesn't do anything. I took it to a shop and they had no clue what was wrong. They told me for starters they would replace the lower intake and the upper plennum. Will that fix the problem?