you dont need to remove the engine to change the oil pump.
you just need to take your radiator/condensor/fmic/front bar off as they tend to need a hydraulic puller to get their balancers off.
after thats off its a matter of removing your timing belt gear, dropping your sump, replacing the oil pump and putting it back together.
it would take a few hrs at the most to get it all done with the right tools.
it took me just over an hour to get my oil pump off (i dont have a front bar on my car), and that included taking my radiator and condensor out and dropping the sump.