My 1965 c10 long bed still has drum brakes(vacuum power boost assisted master cylinder) on all four wheels. I have had my truck since April of 2003 and as long as I keep in mind the limits of it's stopping power, I have no problems unless other people get involved.
As long as the internal metal hardware and springs within the drums are in good shape and the shoes are not worn, you should be fine. Taking into consideration the lines and master cylinder and everything else is in proper working order.
The internal bits and pieces to rebuild the drums are available from parts stores.
Drum brakes when they get wet do take longer to stop. Drum brakes will lock the wheels up on you if you stomp on them, so try to remember to pump the brake pedal if you get into a situation on the road.
As Red58 noted, you could swap out to disc brakes on the front. Most of the kits to swap disc brakes into even older model trucks use a lot of the parts and pieces from the 1967-1972 trucks.
It is an added expense and it is all about if you want to spend the money or not. There have been before and after tests of disc brake swaps on older trucks, with the disc brakes stopping sooner. However, I don't recall reading about any before and after swap tests done with it under load.
Always remember it is a truck, it was designed to haul things under load. It is not a sports car. Let off the throttle sooner and ease into the brakes. When the bed is unloaded and you have to get hard into the brakes because of a situation you will feel the bed wanting to whip around.
Think when you drive and you should be just fine, as long as you keep everything in good mechanical order.
-W
