Caliper upgrade???

The dark in the old brake fluid is rust. That is why your MC failed. In VA, you should be bleeding thru new brake fluid at least every 4 years, in all your cars. Most drivers don't know that and go until they have failures. If you use DOT 5 silicone, no such worries. The factory disks in 1973+ cars are fine. Front disks were a federal mandate, mainly because clueless drivers would ride the brakes all the way down mountain roads until they overheated and went off the side. Disk rotors cool faster than drums. Even today, on the Blue Ridge Pkwy you have the aroma of FL drivers riding the brakes instead of downshifting. The tech is simple - tires stop the car. If the brakes can skid the tires, and evenly, they can do the job. If you aren't over-heating the brakes (get fade), they are big enough. You shouldn't need bigger brakes unless driving like a road racer. One clue is if you get <15 mpg since all braking is wasted energy.