Sicklebar mowers are one of the most sought after attachments for these old tractors.  Though "used and abused" ones can be found, most all are missing the swathboard shown in the illustration from the Operator's Manual above. 

Jason Schaefer "lucked upon" a sicklebar in great shape, complete with the original wooden swathboard.  He traced the original, and Roy Pope kindly volunteered to convert those tracings into dimensional line (i.e. CAD) drawings.  They've been compared to another one, and all the dimensions and measurements seem right, but there's NO guarantees.  Let us know if you try them and they don't work for you, or need modification.