Installed LASCO MagnaFlush Toilet Tank Kit, Now Toilet Runs All the Time?
runs constantly


Generally when someone says it "runs constantly" it means they are talking about the ballcock valve (the fill valve). A new fill valve that constantly runs usually means that the installer did not flush the internal components of the fill valve after installation. Oftentimes debris is dislodged from the supply system (supply line, stop valve, supply pipes) that can affect operation of the new fill valve. It is standard practice for a plumber to open the top of the fill valve assembly and open the stop valve a bit, flushing the new valve diaphragm and washers. In fact I will bet $$ that the installation instructions recommend this.

However, a clue in your post makes me suspicious: 


  turned the water off at the valve at bedtime with the tank full whether it would be full in the morning. Strangely it was near empty in the morning


A leaky fill valve would just run all the time, but the tank would not empty. Now we need to suspect the flush valve assembly (which includes the flapper). You tested the flush valve seat surface with a piece of styrofoam and it did not leak, so the flush valve seal is OK.

So on to the flapper. Generally a bad flapper causes a slow leak into the bowl, resulting in the fill valve running intermittently, to refill the tank as the leaky flapper allows the tank level to slowly drop. The "constant" run you describe would only occur if the flapper was leaking catastrophically (using "catastrophically" in a relative fashion). I suggest you put a few drops of food coloring in the tank, this will immediately tell you whether or not the flapper is leaking (cuz you will see the dye in the bowl).