not sure if i have hydrovac
according to this you did
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0529.htmif it wasnt removed it should be mounted on the inside of the pass. side frame rail just on the other side of the three stacked road flares. behind the seat on the passenger side is where the breather is located for it.
could i just put a dual master off a 79 one ton chevy.
maybe

i wouldnt.
i understand they usually bolt to the booster but is a booster really needed.
my 51 dump's tare wt is 7300 lbs. its gross is 16,000lbs just as yours is. i can move just under 4.5 tons of whatever legally. until you get your tare wt. established you dont know what you can haul weight wise. but let me tell you this. right after i did a complete brake job on the ASHTON (which weighs in 12,000 lbs with no water.)someone if front of me decided to make a left hand turn at the spur of the moment with no notice. i was able to lock up the truck because i had to lock up the truck. i was able to do it on the first press of the brake pedal not the second or third pump. i was making all kinds of hand jestures not to mention what was coming out of my mouth. i looked at my passenger and said boy am i glad i replaced the whole brake system with new stuff

if i hadnt i would have slammed into the back of the car because i would have been too busy pumping the brakes to get it to stop beacuse i didnt restore the brake system as a system but only as a component
now back to your question, YES. your going to load it up wheather its on the back or on a trailer. if its on a trailer then your going to load up the bed to support what's on the trailer. when it comes to stopping your going to need all the help you can get.