Don't push the pedal too far down with the drums off. You could pop the pistons out of the wheel cylinder. Feel around the dust covers of the cylinder. If it is brake fluid, they will be wet.

Did you replace the brake hoses and clean out the lines when you put on the new cylinders? Any dirt, crud, rust, etc... that was there before could have gotten into the new parts and made them leak. Don't discount them as bad just because they were "new" at one point.

My master did a similar fall to useless. I swapped over to DOT 5 Sunday so this new one might actually last more than 4 years.