Hi MM,
Re the big end nut torques ?
Does it take the same ft/lbs to undo a nut as to tighten it ?
I don't believe so? I think that the metal yields a little over time after tightening ??
The Ariel flywheels are cast where as the B44 wheels are steel so friction /grip and yield of the metal will be different
Recently I rebuilt a couple of Indian Chief engines, The torques for the big end and main shaft nuts is 100ft/lbs when the engine has
"Z" metal flywheels, non "Z" flywheels get 70/75 ft/lbs
These pins and shafts do not have shoulders though ( I could go and check thread size and pitch on the old parts if needed)
With shouldered pins the shoulders need to to seat against the flywheel when fully tightened,
a gap between pin shoulder and flywheel when fitted by hand is essential so the grip is taken up by the taper

Final torque value is not a fixed figure I believe
Whatever the nuts need to pull the pins against the shoulders, +
Of course the flywheel taper bores stretch every time the pins are replaced which does not help when fettling old engines
From The figures that you measured to release the tapers it looks like the flywheel bores are in good order though

I prefer to not rely on the mainshaft centres, but set up the assembly on bearings and v blocks instead

I believe it would be very difficult to evenly plate the main bearing ? the surface of the copper plating will not be smooth ?
I believe that you need to plate oversize and machine to the desired figure
I think I would have gone the route of a steel sleeve on the bearing as you had the case set up on the milling machine ??

Always more than one way to skin a cat!!!