Leaking Heater Core...

This is going from memory many years back. On my early A the drains were a sort of slot at the bottom of the fender behind the wheel opening. Taking off the fender should help get a bunch of crud out of there. You might just try shoving a wire up there to break stuff loose. Or maybe loosen the bolt at the bottom rear of the fender & pull the bottom of the fender out a bit to help stuff fall out. Try it while you run some water into the cowl vent. Once you get a good flow of water you can probably flush a bunch of crud out by increasing the water volume.