C 60 brake upgrade questions

[old Chevy guy]

My neighbor has what I believe is a 68 C 60. That is I believe its a 68 its definitely a C 60 . He is asking me how to upgrade the brakes, he says it only has the single system master and wants to have the double for safety. Im surprised that a truck of that year has that system especially that size since pickups had the dual system brakes starting in 67. My 66 C 60 had a brake booster under the cab he says this one does not. Should it or was that an option? What year would have the dual system and can I buy the parts to upgrade it and what would that entail? Thanks for any advice/knowledge you can give me and if anybody needs more details I can go check it out or get pictures if need be.