I have looked but can't find when the oil pan bracket went from 7 to 3 rivets.
I think about 1913.
To expand on what Jack D said. My mostly '13 speedster has what based upon previous discussions appears to be a transitional pan. The arms/hangers are tapered where they sit upon the frame. That makes them like the earlier 7 rivet arms. However, they are both only 3 rivet. There seems to be some question yet exactly when all these changes took place. But apparently, with some varied crossovers, late '12 to very early '13 seems to be the prevailing opinion for dropping from 7 to 3 rivets.
If I recall correctly.
I do hope to read replies from those more learned than I.
Drive carefully, and enjoy, W2
The reason I ask is my B numbered'12 torpedo has the deep tea cup and narrow nose like the typical'12 pan but only 3 rivets. I will have to look at the top to see if there is a taper. I still haven't mastered the art of resizing pictures.
Rivet count is not the only difference between 3 and 7 rivets. Among other changes, clearance between the vertical arm and the pan edge is increased on the later arms. See Mark Herdman's excellent disertation for more info and detail.
I have a pan that there are 7 holes punched in the arms but only 3 rivets placed. Not replacement arms but appear to be original. There were burs that indicate the holes were drilled or punched from the engine side. I purchased this pan for my 12 project through tray so cannot say anything about the timing of production but would expect it to be sometime late 1912.
The front motor mount bracket also changed in 1913. The earlier ones surround the hole, and the later design avoids the hole, and just goes up to it, but still has the brazed on teacup. I believe in later '13, they did away with the brazed on teacup, and went to the '14 style crankcase, but it still has a teacup look.