Jbbies, Chilly 807 is correct, you want MINIMAL weight. My brother used to do a lot of seeding work for the UK Ministry of Transport and used only a panel of welded mesh fencing and dragged behind a Landrover (for speed). He also seeded a new golf course using the same method. I have broadcast grass seed for about 50 years now and originally used a chain harrow (drag type not tpl mounted) flipped on its back so that the teeth were not in use, just the links lying flat on the ground. In latter years I have used only a couple of chains, the links are made from about 3/8ths metal although I have not measured them, and spaced with light angle iron. It works. I will be sowing about 9 acres in the next couple of weeks.
Just for the record, the chain harrow (one is shown in bcp's post) when used with teeth down is for use on grassland, not for levelling. It has two purposes, one to spread horse droppings or cow pats so that they are more evenly spread and incorporated into the soil quicker by our underground armies, and secondly to freshen up the grass, similar to what you would do with a spring tine rake on you best lawn - remove dead thatch and any moss.