I would also suggest asking for the gearbox orientation, sometimes in hard to fit spots one gear orientation may be a better fit than others. But this obviously gets covered when you get all the application and spec information.
What is your application
What speed in rpm is needed to run the machine
Describe the general layout of the machine and how you want to drive the machine
how may hours a day will it operate and will it be a critical operation
what is the supply voltage