Just get the dimensions, figure out where on the front panel you want it to go, measure carefully, then use something round (a glue bottle, I used plumbers tape) and draw the round corners.
Cut just a little outside the line and do a test fit (the design of the coin door will allow for small imperfections but try to keep them under 1/4 of an inch). You will then like need to make some small adjustments.
It's not as hard as you think, just be sure to measure twice (I used the dimensions off of the page you posted).