Converting to Power steering needs the structure from a later Power steering car welded to the bulkhead of the earlier car along with the Rack, front hubs, pump, mounting bracket, belts, pipes, reservoir. It is best done on a stripped car with the engine plus wiring and trim removed from the engine bay and the passenger cabin. I have done it twice and added some negative front camber for a transformation in driving experience and of course easier parking.
You might be better off finding a Corsa B electric Power steering column and adding that to what you have. Car Builder Solutions sell a control box to let you vary the level of assistance so you can just turn it on for parking.
I hope this is of some help.
NB do check the ball joints, strut top bearings, and track rod ends as they can be a cause of much heavier steering.
Eric