I split this post into two parts so I would not loose it altogether. I used to lean out Z cars with the first fuel injection 75-78. My 1976 had no cat or egr and it was emissions legal.
At the time Federal law imposed a $10,000 fine for emissions tampering and $2500 for owner emissions tampering. A law seldom enforced but something every dealer or shop knew could shut them down in a heart beat and have their customers cars confiscated as evidence.
The reason lean burn died was NOX emissions. California VXs had no lean burn and their mileage drop was considerable compared to Federal lean burn versions.
I can understand your position on lower final drive ratios after reading the linked thread or at least part of it. If i need to pass another vehicle I just downshift, get the job done and get back into top gear.
You should read up on Transonic Combustion. They have a patented injector design that uses supercritical (450 degrees f) heated fuel at 3000 PSI pressure that once the engine is warm ignites upon injection without any spark. It is multi fuel capable and I believe it is the current eveolution of old Smokeys work decades ago. It just took that long for technology to catch up with his theorey in a way that is practical and safe.
It's soo good that engine out exhaust gasses require no emissions controls whatsoever.
Truly a homogenous mixture that does not even reach peak combustion temperatures where NOX formation begins and it only needs a spark plug to warm up.
http://www.tscombustion.com/
regards
Mech