Hi there. Thanks for the recommendation.
The MA10 head needs to make its way quickly to the scrap bin. The MA12 head is far better and a straight fit.
The earlier 31B castings are OK but the later cat model, 18B are probably better still.
MA10 flywheels are lighter, MA10 fron pulleys are lighter and all are interchangeable.
If you have flywheel work done (anywhere) make sure you get it dynamically balanced