tlorber:
You have the same engine that Canyon has. Even though the middle digit in the serial number might be an I, it would still be translated as a 1 (I guess it depended on who stamped it), so the build date would have been 8/14, or August 14. It could have been cast and built in '56 for the '57 model year, or it could have been built late in the '57 model run. The date code would tell. The 3837004 block was used '55-'57 according to Inliners.