Yes, the 1937 engines tended to have castings that had impurities. In 1938 Lionel changed to a different casting vendor. Seems like the 38-42 were okay. See DON HODOR’s two VIDEOs ON AMAZON PRIME. he was the expert on the 700 and 763. The castings warp, crack, grow or shrink! All my info is from those videos.
the 700 and 763 are exactly the same casting. The 700 just had added on parts, like piping, coupler lift bar, etc.
