I have an aftermarket one installed in my 64, it was such a butcher job, I removed it and may not reinstall it. I had RichL79 email me a copy of a diagram of one for his 65, you might try to email him too.
I don't think there ever was an RPO for it. It was only dealer installed as far as I know. It was available in 1964 on all GM A-bodies. Various versions were used and the Buick and Olds versions used unique wiring plugs while the Pontiac and Chevy versions used the familiar half-moon style plug which matches the steering column plug.
E-mail me if you need pictures. I have a very good one that came with my car that I have not installed because it gets banged by my knee if it is in place.
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