Finally got this as near to acceptable as I can. It's still a bit squirrelly, but the BF-109 was like that in real life.
I thought had to set the values unevenly to make the plane rest evenly. That worked but take-of and landing were still uncontrolled. Eventually, I found settings that could be equal on both sides and also correct the extra long right landing gear. Here are the old and new settings.
ORIGINAL
[LeftMainGear]
ShockStroke=0.20
SpringFactor=2.0
DampingFactor=2.0
RollingRadius=0.292
[RightMainGear]
ShockStroke=0.20
SpringFactor=2.0
DampingFactor=2.0
RollingRadius=0.292
Even though the values are equal, this produced a right gear that was too long and uncontrolled handling on the ground above 40Kts.
So I looked up Migbuster's guide to correct the right gear. No matter how much I adjusted the rolling radius it wouldn't move the wheel "out of" the tarmac until I adjusted the shock stroke to a very low value. Incidentally, you shouldn't adjust shock value below 0.01. The plane and the AIs will just flip over and blow up. Eventually, adjusting the shock stroke to the same low value AND the rolling radius to the same lower value got the result I wanted with balanced values. Here's the new settings.
MODDED
[LeftMainGear]
ShockStroke=0.02
SpringFactor=2.0
DampingFactor=1.0
RollingRadius=0.279
[RightMainGear]
ShockStroke=0.02
SpringFactor=2.0
DampingFactor=1.0
RollingRadius=0.279
This is still not perfect. Spring factor adjustments help, but unequal ones cause spontaneous bouncing in one direction. So prefer to keep them at the original setting. The plane still veers a bit, but at least it's controllable with rudder adjustments. The AI are able to take off normally.