Those are more than likely Pequea brand. I sold their products. Their ground drive unit does not use any gears that I know of. I think they are all pulley/belt driven. I only sold the PTO driven units. HE maybe better off switching his over to PTO drive. All he would need is a right angle gear box and some shafts.
Here is the contact information for Pequea:
Pequea, A Skibo Company • 200 Jalyn Drive P.O. Box 399, New Holland, PA 17557 • (717) 354-4343 or toll-free (866) 684-0393
Here is pictures of the ground drive and PTO Pequea units.