Well see if this one is closer.

#40 Roller Chain 1/2" x 5/16" 43 drive links. The other chain was probably a 3/16" version for the non differential models.

Stockman 231901

or

Stockman 231901 chain

IPL Manual Download

22-25I3-25E94-25K94-25H94-25C95-25K95-25K96.pdf

Take with a grain of salt as I am a few skips and a hop from the there.