I applaud your efforts. They seem to be well thought out, and practical (cept for maybe the grounds which seem to be a waste of weight to me.. just clean up your ground cable(s)?)...
Its shame at the grassroots level we cannot be more scientific in measuring results.. its just not feasible as you point out.. not to mention, filling a tank the same each time is not even feasible.. its one of the items Id like to get a handle on.. just got 48 mpg last tank in my 90 HF.. but it was getting 42.. was it better fuel? Better driving? Or did the pump shut down early? With such a small tank even a quart can impact... ugh.. so what you are doing.. (charging ahead) makes the most sense.. well done.
That's why we focus more on the 90 day average on this site. Minor hiccups like overfill/underfill and such are averaged out over 90 days and are negligible. If you are looking for instant data as to driving technique and such most vehicles now are compatible with a ScanGauge which can give you that live data from the engine computer.
when you grounded that bolt on the exhaust manifold, did you make sure to remove all the rust from the nut, and the bolt itself? Also, can you do us a favor and tell us the OHMs value of the o2 sensor to ground? My suggestion is to use one probe on the body of the o2 sensor (anywhere there is metal) and then some ground bolt that is on the car, make sure the bolt is COMPLETELY clean both where it screws in and where you make contact with the probe. Report back the ohms value you get.. I'm gearing up for a thread on o2 sensor grounding.
The threaded stud and nut were both clean on their contact points when I installed it.
Prior to installing it, I had 0.00 from the body of the 02 to negative battery ground. There was no difference between installing the wire and not having it. (as far as the multi-meter was concerned) I suspect my multi meter just isn't sensitive enough.
However, I had already installed a couple of extra grounds to the block from the battery prior to this ground. Those were probably the actual fix.
All I can say about whether or not it works is that it can't hurt. There were no quantifiable results to speak of. The "seat of the pants" feel made me think it was different, in the good way, but nothing I can test scientifically other than the multi-meter.
I'd suggest that people use a multi-meter on the body of the 02 to the negative lead on the battery prior to adding grounds/cleaning things up. If there's no higher resistance to ground, I'd say adding extra grounds would do nothing but add weight.
If, on the other hand, there was even a slight amount of resistance, it would be well worth someone's effort to correct it, for obvious reasons. I guess that's where I'd focus.
Anyway, hope that helped.