The design of the three speed Indian transmission changed very little from the 1930's until 1953. Externally the case were beefed up in the early 40's. This meant that I need the less reinforced design. The transmission case on the left (clean) is a late 30's "ridge" case and the transmission on the right (dirty) is a post war transmission case.
Note the reinforcement band on the right. A common place for these transmission cases to crack is below the rear mount. Likely from the rear mounting bolt loosing up and allowing the case to pound against the frame.
Note the beefed up upper left mount on the right case. This would interfere with the chain guard on a 37 chief.
Not much different here. Note the mounting hole on the flange in the 5 o'clock position. If the mounting hole is in the six o'clock position that indicates the case is an late 20's / early 30's case. Also note the two holes on either side of the lower large hole. They allow oil to pass freely between the transmission case and the primary. In a 1940 case these holes are absent to allow running different oil in the case and primary. Some plug these holes so that they can run a lighter, multi weight, oil in the primary (10w-30) and heavier oil (50) in the transmission case.
Note the reinforcement buttress on the right on the tower.
The tower caps differ slightly as well as the location of the number on the casting.
Lastly you can get an overdrive four speed transmission http://www.chief-overdrive.com/
. This really beats the hell out the factory three speed "Crash Box" but not the right transmission for and points bike.
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