Here's an oddball thought:

Many current vehicles have small pre-catalytic converters, followed by the main cats. They also have O-2 senssors before and after the cats to monitor how well the cats work. I'm wondering if anyone has ever installed a late style pre-cat on a Camino and then put the O-2 sensor right behind the pre-cat. Doing so would feed the O-2 sensor a cleaner mixture than what is actuallly leaving the engine and may cause the computer to both advance the timing and richen the mixture. At the same time, the exhaust would be "correct" for the main cat, so it should pass smog just fine.

Anyone tried it or heard of someone doing it?

I would not think this is a good idea. The computer in our cars is designed to read that O2 signal, and then adjust the mixture to try and achieve the perfect 14.7/1 ratio oa air/fuel. If the signal you send the computer tells it that the mixture is too lean, then it will richen the mixture. However, the extra cat will likely burn off all of the extra fuel in the exhaust, so that the computer will continue to demand rich until full rich, all the time.

A lot depends on how well a pre-cat can clean up the mixture. While 14.7 is the ideal mixture, I think the the computer is actually shooting for the lean side of the mix.

Seems like the only way to really know is to try it on one of the cars. Not sure how the answer could be verified except with an after market O2 sensor and gauge.