Rear drums of a similar size hae been used on more modern, heavier, and faster bike than the Bullet.
Besides, the front brake is much more important to stopping power, that's why manufacturers went to front disks land before adding them to the back and why so many cars still have drums in the back.
As long as it is properly adjusted the existing rear brake should provide ample stopping power.
I just love being told things like that. It is a pleasant and long winded way of telling me I am wrong and that my rear brake is really fine - I just don't know it.
I have taken the rear wheel off and used the opportunity to center the brakes better. I have adjusted the various adjustment points so it's back like factory. The fact is, there is a tremendous amount of flexing in the connection from pedal to brake arm. The whole thing is whippy and feeble. The actual braking force delivered by the brake which many have said is large enough to stop an old Duo-Glide, is weak. Amazingly so.
I understand the relationship between the front and read brakes. True, the front brake does the majority of the stopping. However, on gravel, sand, wet leaves and many of the other road surfaces one finds here in the Midwest, a good back brake is helpful in keeping the bike upright.
As I ride the bake more, either the back brake is getting slightly better, or I'm getting used to it. Not sure which. One thing that I am sure of though is that I now have to plan ahead for intersections rather than just zooming up to them and knowing I have enough brake to stop in plenty of time. But truly, the Bullet is so much fun that I don't mind the marshmellow rear brake quite so much.