I have always known that a cold engine should be completely warmed up  to prevent premature rusting of engine and exhaust components from condensation.

The heat riser valve is on the pass. side of the exhaust. It basically blocks most of the exhaust flow from that side until the engine warms to operating temp. Your's is controlled by vacuum, while the older cars had a bi-metallic spring that would open the valve as it got hot. No exhaust flow = no condensation on that side.
The heat riser is one part of the exhaust cross-over passage in the heads, and intake manifold. It re-directs the exhaust flow from that side thru the bottom of the intake to heat it up quicker, thus reducing exhaust emissions.

Sorry Joel......I failed to mention, no heat riser either.,,,,,ahh,,,a least I don't think so. I just glanced down and it appeared to be a direct exhaust-manifold bolt-up with no HR valve but I didn't inspect closely.......I know it's not there.....99%.

Mine does this too Rich an I know it isn't a heat riser issue. (I have headers.)I always assumed that it was the pipes sweating as the cold air and the pipes themselves began to heat up. This wouldn't account though why it doesn't occur as prevalent on the passenger side.

Thanks for posting this up I had always wondered about it when I was behind the car at start up. I just never remembered to ask about it.

Hi Larry...

The 71 does the exact same thing.

Ditto Rich, I have the same game plan. Only variation is the Blacray will be getting new shocks, shift kit, and a chrome tranny pan for sure. Everything else gets scraped, brushed, sanded, repaired, replaced , and painted.

Ah.... the smell of fresh paint in the garage... An the pain of sore muscles from rollin around. Ain't it fun ta get older.....

[QUOTE=jayare] Hi Larry...

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As Joel said, I'ts gotta be circulating the warm moist air through the intake manifold to the driver's side.