the 6 speed box is bigger (read longer) than the 5 speed, so on a cento the wheel hits on full lock thus you need steering lock reducers on to stop the catching. Loads of room in a mk1 bay though so sure it'll be fine. On cento you also have to change the selector mechanism over and i think the driveshaft cups. I never done it though so this is all from memory of what i have read on here over the years. So some of them things might need swapping over as well.