Drawing the radius is easy, you just tie one end of a piece of string to a sharpy,and the other to the hub
Keep tension on the string and you get a perfect radius everything
Just cut it out with a sawzall (stay within the lines) and trim with the grinder
On a sidenote, is the dart custom 5 on 4 or 5 on 4.5?
It may be old enough to still be 5 on 4, in which case the rims from the dart sport won't fit