The crankshafts look as if they are forged, and the number on each may be the number of the forge die that was used. They are not plant numbers.
The engines were sold with a choice of output shaft lengths, and sometimes diameters. The type and position of keyway could also be varied. There may be other variables as well. I have not found a simple, comprehensive comparison of Briggs PTO designs comparable with the ones in Honda workshop manuals.
