It would INCREASE the value to add disc brakes.
Use a quality kit from ECE.
www.earlyclassic.com
They make conversion spindles now, for the 63-70 trucks.
Don't get conned into using 71-72 or 73-87 spindles.
Thats NOT required anymore.
You can add stock or dropped spindles also.
That's also a good time to get all the balljoints and tie rods.