Actually the Grange and Manor class locos are very different. The Grange class of locos is a derivative of the Hall class locomotives with a smaller driving wheel diameter, 5'8" for the Grange and 6' for the Hall. Their are other detail differences between the Hall and Grange class locos. When calculating tractive effort for a steam locomotive weight has nothing to do with it. The values required used for calculating tractive effort are boiler pressure, piston diameter, piston stroke, wheel diameter and a constant. The constant changes between country's and builders, Mainline UK railways used a constant of 0.85, Industrial railways usually went for 0.6. The constant represents losses in pressure and friction.
Rob