The Daysailer 3 rigging has me confused. It is the first sailboat I have seen that has the main sheet mid boom with no traveler or boom vang. For now I am planning on sailing in very light wind so I am hoping it wont be a problem.
You don't have to stick to the factory rigging for a DaySailer.
One thing you might want to do is rig your own vang. It's not that difficult and will improve your ability to handle gusts. Another thing you might want to do is add (or have a sailmaker add) a set of reef points to your main, and then rig a reef hook and reef line for a jiffy reef. That would improve your ability to deal with sustained winds that are too high for the full sail.
About your original question:
Does anyone know if the clam cleat belongs on top of the tiller or underneath.
Whether a line is an uphaul or downhaul for a rudder is decided by whether it pulls up on the leading or trailing edge of the rudder, not whether the cleat is on top or underneath the tiller. There has to be a way for the pull to turn 90 degrees from up to forward; sometimes that's done with a cheek block on the rudder head, sometimes the line goes around a pin or through a hole. Without pictures, it would be difficult to advise in your specific case.
I have so far not fitted either one of these lines and am relying on friction (works moderately well below planing speeds). The main reason for me is that I want to be able to raise the tiller, if necessary, in case something or somebody is in the way when I have to make a sharp turn. There are clever ways of rigging a downhaul so it does not pull down the tiller, but most systems I've seen are not clever that way.