Will a 5 speed mk3 fiesta gearbox fit mk2 1100cc?

No, a 5-speed gearbox from a Mk3 Fiesta will not directly fit a Mk2 1100cc Fiesta. The bell housings are different, meaning the gearbox won't bolt up to the engine. There are significant differences in the transmission mounting points and the input shaft. You'd need significant modification, likely beyond a reasonable DIY project, to make them compatible.