All the fuel injection companies use 2 types of calibration fluids. For regular production work the Rock Valley Viscor 16A and 16B are regularly used (there are other suppliers as well) for safety reasons. However, the viscosity and density are not the best match to "gasoline" and thus flow ocorrection factors must be used if absolute accuracy is required. For more accurate work, you need an explosion proof test rig and either n-Heptane or Indolene. N-Heptane can be filtered and reused because it is a pure substance. Indolene is your best match to "gasoline" but because it is a blend it can only be used for a single pass and then discarded.
I found this formula
One cubic centimeter per minute converted into pound per hour - Gasoline equals = 0.098 lb/hr
1 cm3/min = 0.098 lb/hr
or 428*0.098 = 41.944

The correction factor of 16b fluid is not known so you may make a research.
1.035 scalar is for N-heptan which is not applicable to you, since the injectors are tested with 16B fluid.

is some oscillation in the PW at low load
If the spread between the cells[on both rpm and map vectors] is not optimal and polished it can result in constant oscillations back and forth.
The best practice is to keep constant rpm and map 2000 and 40 for example and tune with wideband.
Very hard to achieve on the road though. If you can access a load dyno you will be done real quick.