If it crunches going into gear and still drives, it needs a synchro...if it grinds and has no drive the synchro has gone and worn all the teeth off the gear or selector hub.and the synchro,sliding sleeve,and gear all need to be replaced,(not cheap) or get a gear box out of a mk2/2b which fits and drops revs by 500rpm at 70mph(if yours is in fact a Grande Punto) . (Check clutch fits on gearbox spline before fitting)
you sure it fits? grande gearbox got different mounts