Per my experience, most steel FWs with the same number of speeds, weigh very similarly. I don't think the little difference between them is ever going to be noticeable on the road, so picking your steel freewheel on the basis of weight is a bit pointless. I still think that hybrid Al (cogs)/Fe (body) FWs is not a bad way to go if you want to lose some weight. At least you won't have to worry too much about stripping pin wrench holes or notches on them, if you have to remove the thing from your rear wheels. The Zeus 2000 FW is a good one, and the Al cogs for them are still available from sellers at eBay.