You will find that the link will depend on the spring you have. I make them out of 1/16" stainless steel strip 1/2" wide.
One bike has a length of 1 1/2" and the other 1". Drill 1/4" clearance hole in one end for clevis end and clearance hole in other end for spring wire. You can take a rough measurement for length with the spring hanging from the switch.
Near enough is good enough as you can pivot the link to take up the slack.
Radius the corners of the link and you will be happy with the result.
Trev.