Don,
That's a rear hat style rotor from a 77-79 Caddy it fits on the original 64 hub. Its part of the old style Scarebird disc brake conversion (the best!).
The wheels are vintage American T-70 I now have after market center spinners I bought on E-Bay.
I lucked out and picked up five wheels. The spare didn't balance well but its in the trunk anyhow.
Since my 462 install I take my car up to 145 mph. So I'm switching to stock steel chrome rims. I just don't like going that fast on old aluminum wheels even though they are as smooth as glass.
That rim you have is rare. Terry at AKH might be interested in it.
http://akhwheels.com/