Typically, it's a bit tougher to "lock up" disk Brakes, but that, alone, isn't enough reason to go that route.
You always hear the argument that 80% of your braking power is in the front wheels, and that is very true. In all the years I drove beetle sedans I changed front shoes every other year or so and never changed rear shoes even once. Same thing on all of my cars - almost never touched the rears.
That said, the only advantage I can think of for rear disks on speedsters is what Jack Crosby keeps telling us - the car will stop in a straight line with no pulling to one side or the other if you have disks all around. Very true.
Ford must be convinced of greater stopping power with rear disks, because my last pickup (F150) went from rear drums to rear disks when you ordered the "trailering package", so those crafty designers had to know something I don't.
One thing I found that increased drum stopping power is an 11 pound residual valve between the master cylinder and the rear brakes. It holds the shoes a bit closer to the drum when off-pedal and gets the shoes to engage sooner with a bit more pedal-power (it seems to me, anyway). A residual valve is not needed on rear disks.
This help? Gn