A few STL models were uploaded as well as the SCAD file.
Open the file in OpenSCAD and load the library mentioned from the original.
Then just change the parameters.
Beware that it will easily grow to be bigger than a MK4 bed.
I had a couple of coins there different sizes so I put a piece of filament in the bottom of a bigger slot to hold the coin higher.
The author remixed this model.
Modified to be parameter driven for number of coins, coin size, spacing and back height.