I'm guessing we are talking about your 49 3/4 ton.
I would say go with the dual master cylinder setup and stock brakes. I think you would be very happy with the power brake version of it that virtually bolts in place under the floor. I say VIRTUALLY as it really requires a little bit of fabrication to make it work. In the long run it will be safer, allow you to stop faster, and replacement parts will be eazier to find. To my knowledge there is no disc brake kit offered for the 3/4 ton. Best you can do is swap out the backing plates from a later 50s truck and upgrade to the bendix brakes, without to much fabrication.
John
