What's the difference between a heavy Mikado and a light Mikado ?... - Model Railroader Magazine

I believe the Kalmbach Model Railroader Cyclopedia Volume I, Steam Locomotives can be considered authoritative. It states (page 73 in my 1960 edition) that the light and heavy USRA Midados used the same 63" drivers and running gear but had the following differences:

Weight on drivers, lbs: Light, 224,000 Heavy, 240,000
Tractive force, lbs: Light, 54,600 Heavy, 60,000
Grate area, sq. ft. Light, 66.7 Heavy, 70.8
Cylinders, inches
(diameter & stroke) Light, 26 x 30 Heavy, 27 x 32
Boiler diameter Light 86" Heavy, 96"

John