Do you have to take the engine out to replace the heads or plugs?

You do not have to remove the engine to replace the components you are asking about. However, it would be far easier to disassemble the engine outside of the vehicle. As an added note: repairing cylinder heads and block on this vehicle would require a professional engine rebuilder and machine shop. Troubleshooting while still in the vehicle is essential.

You seem to be a little confused as to what needs to be done here .. An engine oil pressure problem isn’t related to the “heads or plugs” - - Highly recommend seeking *hands-on* assistance from qualifying personnel.