Buy a wrecked donor Focus with a Zetec engine, and replace your SOHC with the Zetec. I have a Focus LX that a prior owner did this to. The swap is easy to do, the Zetec bolts right on to the MTX transmission and you just need to take the engine computer and wiring and such from the donor car.
Don't just replace the head on the SOHC. When the valve seats drop metal particles are blown into both the intake and exhaust. All of those have to be cleaned out or the engine will fail again when those particles are sucked into the repaired engine.
There are aftermarket valve seats with a different metal formulation that won't fail, for the SOHC.