The reason why disks became more popular than drum brakes is because of heat dissipation. Friction makes heat. And the system better able to shed the heat is the big open air disk.
NASCAR used to have the big cars with drum brakes. The drums would turn cherry red under heavy braking. They would put air ducts on the cars to route air onto the drums. They would also increase the width of the brake pad to 3-4 inches. Further they would use a ceramic pad so the heat could go inward through them into and out of the brake shoe in that direction instead of only toward the outside of the drum.
Where you need superior cooling it is under heavy braking conditions. Drum brake have both speed fade and heat fade. The space between the pad and drum generates a gas expansion that acts like hydroplaning and keeps the pad from full friction contact with the drum surface area. The result is that drum brakes stop working when you need them the most.
The front disk was put on the front of the SOHC4 because it performs better than a drum brake under heavy use conditions.
Unless you are making a vintage replica bike that originally had a drum up front, or are making a garage queen conversation bike that will NEVER see high speeds/repetitive braking cycles, or actual track conditions, then use at least a single disk brake up front.
If you want it to look like a real racer then use a bigger disk, dual disk, and/or calipers with multiple pistons in them.
It's a matter if you want looks or real real race function.
Cheers,
