Maybe too late for you, but there is fundemental point in mechanics that ought to be addressed.
It is not due to the weight. All the drum brakes on the a-bodies (and probably every production car of that era and newer) self assist. These are mechanical arrangements of the shoes to the drum known as servo or duo servo. All other things being equal, a drum brake car will require less force on the brake pedal to stop. This is why cars with front disks more frequently were (and are) equiped with power assist than cars with front drums.
This also leads to another point which is worth mentioning in relation to another question in the opening post.
It is very important that the coefficient of friction is very consistant throughout the operating temperature range. If the friction goes down as the brakes get hotter, then the self assisting action becomes less. When this happens the driver has to harder and harder as the brakes work less well.
I don't know what new formulation people were mentioning, but a many brake linings sold aren't that good. On the lining's edge, or on the back of the shoe or pad is almost always stamped an 'Edge Code'. Within the ede code are two letters that very roughly represent friction. If the letters go down, this represents a lining that has less friction as it gets hotter. Do not use this for a drum if you can help it. Examples will FE or ED. You want EE, or better FF, GG, or HH.
So, yes you can have a very good drum brake system but it needs to be adjusted right, has decent linings, and it helps to have the shoes arced if the drums were ever cut. Because the reduced swept area of the smaller drums that came on some of the a-bodies makes it harder to keep them from getting too hot on repeated high speed stops, they're not a good starting point. Agreed that for the same swept area, a disk brake will be better in getting rid of heat. High speed stopping and weight are the main factors in generating heat.