From an economic standpoint the disc swap will probably be the cheapest, even after you add a 2# resid valve and whatever other misc. parts you'll need.

I'll just throw out another alternative though not the cheapest. Speedway also sells repop "Lincoln" drum brakes, which is to say they're self energizing Bendix style that fits with your current hubs and drums (assuming they aren't your problem). They're 12" rather than the F100 11". They are available in 1 3/4" width shoe to match your stock ford stuff, or for the higher zoot approach the 2" wide shoes for use with the aluminum Buick drums. They get $400 for the pair of backing plate/brake assy and if you order by 1/11/09 they pay the shipping (might check if that applies to Canada though).