The D20 engine is the most abundant Focus engine and you can easily and inexpensively find one to replace yours if it is shot. Rebuilding it might actually cost more than just a simple swap. You can find these engines for just a couple hundred or so.
05 ZX3: Steeda intake, 67mm TB, custom 2.5 Magnaflow exhaust, Tom's Tune.
New: 04 SVT : K&N panel filter, 3 performance motor mounts, Taylor wires, orp, 67mm TB, Tom's Tune.