This is a "Farmer's Friend" three pt spreader, same basic design as a Tarter, double gates, iirc on them. No spread chart that was readable when I bought it used. A sticker on it was from a auto dealership in Meridian, MS iirc. Dead end lead.
I had never spread clover before, ever, not even hand sown, so I was surprised at how small it was. Guy at the feed store told me to open the gates about like a toothpick. I fiddled with them, couldn't hardly see it going out to guess spread width, and I was standing next to the spreader moving gates open and closed. Couldn't hardly see it at all, just had to look on the ground and seen some out 12 or so feet each side, so I went with 25'. I had it on the third hole, will move it back to two and try again. Four mph is plenty fast, for the ground is rough in places, but I may have to speed it up some if I can't get the gates right.
The sand idea, will the clover seed and sand not segregate by the time I get it spread?
The blocking off is a good idea as well. I may have room to tack some sheet metal in there, if the whirligig in the bottom doesn't come too close to the gates and hit it.
I am trying to put down five, but if I could get it to 8lb/ac then I would go with that. That is what I have seen recommended in places anyway. I have some wild white clover in there but I wanted to try this and see how it works, if it works. Went with red clover so I can tell what it did.
One other thought, the spreader bats/paddles are rough with surface rust/primer. My thoughts were that would throw it farther, but I may have that backwards. Any reason to shine them up with a wire brush?