Ahhh, yes!!! Someone else in my boat, although it seems you now have an amphibious Falcon too!!
I FREAKIN' HATE FLOOR PAN LEAKS!
Check out this link to my gallery! A gutted cannibalised view of how to fix a Falcon leak!! It's not an easy job.....but now I enjoy wet days.
The water comes in the from the outside air-vent where the wipers are. It then flows into channels on each side of the car exiting via little 5 cent piece holes just infront of each front door, behind the front fender. The drivers side is a very NARROW channel and is easily blocked. It may look like it comes from where you described, but mine was leaking from up under my pedal box - the MOST inaccessible place on the car. My passenger side had a fist size rust hole in the water channel.
25 years of leaves, dirt, mud, gravel and RUST blocks these small pi$$ant holes. You have to CLEAN IT OUT and then block the rust holes somehow.
Take your front right fender off (5-10 min job), remember the small nut inside the door hinge area up near your side rear vision mirror. You will now see the small water drain hole. Get a LONG coat hanger wire, bend a small loop/hook in the end and start fishing for mud! Pour a big glass(es) of water down your vent to assist in flushing it out.
I used selastic/silicone sealant and glued in a big plastic patch. On the drivers side I had to mould in some small fibreglass sheets to rebuilt the rusted out water channel.
ps: I couldn't put the damn dash back in, so built a new one!