1963 steering column to firewall seal
The steering columns are interchangeable 63 to 65 except for the turn signal wiring plug, but the firewall itself is different and, as you've noticed, the 65 gasket has three holes, while the 63 has four. I don't even remember where I got the gasket for my 63, but I made one for my 65 back when it wasn't reproduced. But I can't remember where I got the material to make it. I do remember that it had a color pattern on one side, and the other was white. Not noticeable unless you look really close as only a little bit shows.
Anyway, I think your idea will work. Mostly the gasket is just sealing dust out; don't think much if any water gets into this area.
63 Valiant
65 Barracuda
The steering columns are interchangeable 63 to 65 except for the turn signal wiring plug, but the firewall itself is different and, as you've noticed, the 65 gasket has three holes, while the 63 has four. I don't even remember where I got the gasket for my 63, but I made one for my 65 back when it wasn't reproduced. But I can't remember where I got the material to make it. I do remember that it had a color pattern on one side, and the other was white. Not noticeable unless you look really close as only a little bit shows.
Anyway, I think your idea will work. Mostly the gasket is just sealing dust out; don't think much if any water gets into this area.
63 Valiant
65 Barracuda