As far as all cylinders running even A/F ratio's, I run a stand-a-lone A/F gauge on my 250 engine with a single O2s in the down pipe. I have my dual Carter W-1's set up for 15 to 16 ratio when running on level ground at 65 mph. It varies up and down but averages out around 15.5. The lower speeds always stay above 14.7, with idle at 15.5. With dual carbs placed between cylinders 2 & 3 and 4 & 5, I am getting pretty even distribution. I recently install a stock single carb intake with a stock Monojet carburetor that came off the engine when I pulled it from a yard years ago. The A/F ratio's were off the scale, 18.0 or higher, yet the truck ran fine, just as GM set it up. I tried to richen it up to get the ratio's down, but the exhaust smell was overwhelming rich. The high ratio's were due to the poor distribution, I'm sure the outers cylinders were lean and center was rich, but thats just the way they run. I would bet money, every inline has the same issues. I switched back to the dual setup, 300 mile round trip last weekend, 65 mph interstate ( fairly level both ways ) 18.5 mpg average. If it would only start like fuel injection, I would be happy.
