fitting the 2.0 zetec is gonna be a hell of alot easier as you have all the parts you need on your rs1800 engine to complete the swap. to fit the 2.3 youl need a donor rs2000 for engine, loom, mounts, gearbox, basically everything, then a 2.3 bottom end from a galaxy or scorpio. then modifying the 2.3 to fit (balance shaft/sump mods). and will end up with a powerful albeit very expensive time consuming job. let alone heavy. (cue understeer and need of big brakes. The zetec will be quick to fit, cheap, lighter and cheaper to tune. plus the 45s will go on a treat and no need for aftermarket management as you can use the standard setup to run ignition. I recently did this swap on an rs1800 in 2 days in and driving.