I don know what im doing!

So i bought a 65 mustang. Its in really good condition. Im having trouble focusing on a starting point. The car is mostly stock with the exception of a aftermarket casset / radio player... 200ci inline 6 all drums. Single master cylinder. The car drives and idles smooth. Brakes work just fine. Took it up to 50mph and it stopped well. To me i decided to focus on the brakes im doing a front converion 4 lug disc brakes and keeping the rear drums just replacing all the pieces of the drum breaks. Back plate springs pads adjuter arm. All of it. Im still waiting for everything to come in. So in the mean time i decided to rip out the interior and after i ripped the carpet out i noticed a rust hole in the front passenger floor pan. I stsrted grinding away initally with a metal brush on my drill. And started scrapping away some weird stuff that didnt look good. Which later i found out was the seam sealer. Im worried aboutthe parts i scrapped away exposing the bare metal starting to rust while i wait to get the passenger floor pan cut and welded. I would like to do myself but have no idea what im doing. What should i do with the interior floor thats still good while i wait to get the floor pan cut and welded? I know its alot but if your with me for this long i added pictures in the order of the story. Please help i dont know what im doing!
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Welcome and HNMD (happy new Mustang day)!

I had a Ranchero with similar issues. I always thought along the lines of sealing the area against potential exhaust fume and water intrusion…until new panels are welded in. If memory served, I used some small lightweight metal panels (scraps I had) and 3M strip caulk. Something that wouldn’t be a complete mess to clean up later to facilitate welds. Whatever the panel, it should extend beyond the rust bc sticking anything to rust is dicey.

There are other solutions that come to mind…but none stop the rust and all make a later clean and prep more difficult. Hopefully, some will have better solutions.
 
He would say to get out the "cheek poker" and clean it all up.

Spray it.

Screw down some old license plates to cover the holes.

Spray it again maybe smear some body sealer around the plates.

Order a a brand new trunk liner to put in over the "repair". :)
 
When has anything been one a d done?
Now you can clean and prep and then POR15 the whole floor until you're gonna weld in new metal.
So ooo more like five anddone.