[Mart]

The original question was which is better. Disk brakes are better.
Is a dual master better than a single? Yes if it is a factory designed unit with all the built in extra travel available at the pedal to make the remaining circuit still work if one should fail. You probably wouldn't have that in a conversion of an existing application, especially one with pedals that go down to the floor.
What is your intended usage? That is probably the most relevant question. Just pootling around the local area? Or high speed runs on busy highways in rush hour.
If just pootling, then it may be ok to just stick with drums.
If multiple stops from high speed are envisaged then go with a power disk conversion.
Do you have a lot of experience driving this truck? Has it actually scared you? Are the brakes in good condition? Or are you worrying about a scenario that hasn't happened and may never happen if the working envelope of the vehicle is taken into account?

If it were an open wheel hot rod and looks were paramount, then sticking with drums is normally the obvious choice. But in a fully fendered pickup then a sympathetic conversion to disks would be unnoticeable and would probably be ok if done correctly. The main thing to consider is increasing the track width. A conversion that has minimal track width increase would be better.

You have the answers to the questions and should be able to make an informed decision.

Mart.