This blower should be model number 085040.
If it is serial number 6600 or higher, there are 3 part numbers.
The inner tube yoke (the part that is nearest the center of the driveshaft) is Jacobsen-Ransomes part number(NNN) NNN-NNNN
The outer yoke (the part that connects to the blower shaft) is part number(NNN) NNN-NNNN
The entire half shaft is part number(NNN) NNN-NNNN
If this is below serial number 6600, it is a Haynes-Dana PTO and there are several part numbers.
The shaft/inner yoke is Jacobsen-Ransomes part number 333454.
The u-joint cross is part number 155490.
The outer yoke (attaches to the fan shaft) is part number 347332.
The entire half-shaft (both yokes and the cross) is part number 156258.
All parts can be ordered directly from Jacobsen-Ransomes on EMPART, but they will be much cheaper through NAPA.