Old Gray: It is better to refer to someone by "handle" also. Like bartamos or btzguy. The title under their name is just a indication of how much they post on here.
You are correct about nothing to measure off of. A template needs a "reference", either a point, edge or other hole indicated on the template so that it is put in the same place on both trucks. In your case, all your other factory firewall holes are covered up I guess. As Pete says: finding another truck in your area is best so you can make the template yourself and find a common place that is still available on your truck. Just my 2 cents.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn