I would agree that going 60 in a truck that was designed for 45 wouldn't be a good idea!
This statement only really applies if you will be running the truck fully loaded at a higher speed. The truck was designed to stop fully loaded going 45-50mph. If you are running empty, or nearly empty for a 2ton anyway, at 60mph why do you think you would need to upgrade the brakes?
As to the dual master circuit....also I would say this is an unnecessary upgrade if your emergency brake is in good working order. Brakes rarely catastrophically fail, normally they will leak and slowly loose fluid over time. With proper maintenance the original system should be fine.
Just my 2 cents...but I believe way too many people modify old stuff because they feel they have to to be safe or reliable.
