Just don't put a cheap Shimano Tourney on it... They're heavy crap. I've used the SunRace pictured below on an old Bianchi and it worked well, was lighter than the cheap Shimano freewheel and had much better construction as well...
Image provided by Asama, a cheap Canadian Bike parts wholesaler...
Others have mentioned IRD - I haven't personally used them so can't comment... But I understand they're made fairly nice...