If the hub is truly 120mm (like the one below), then it won't work with a 5-speed freewheel inside dropouts spaced to 120mm -- there won't be enough room for the freewheel.
Freewheel hubs are usually about 110mm wide before adding the axle spacers needed to accommodate a freewheel. If the hubs you're talking about are ~110mm and have that extra ~10mm of spacers on the drive-side, then you should be good-to-go.
