[Espeefan]

Alfy, you can put that pinion on either way, as long as the set-screw doesn't get in the way of the spur gear on the transmission. I usually see guys flip the pinion so that the set-screw is in the rear, torward the bearing of the shaft, but if the shaft is offset to far forward for the pinion gear to mesh properly with the spur gear, then no harm will be done by installing the pinion gear the way you have it. Just depends how long the GRU's shaft is, and how well the pinion gear lines up with the spur gear.