I was going to say there are two options.
I agree with Hachiban in that the balls will be delivered from the hole. In proportion, it looks like you have a two inch roller or maybe a little more depending on desired compression.
As for mounting, I would say you're more likely to mount it on the bottom since that angel creates too much of an arc (imo) but you could also be mounting on the top.
As for a gathering system, that I don't know

__________________
Caio Tenca
Software Engineer
Founder of Washington SWAT Robotics
Ex-Team Manager, Mech. Leader of Westview Robotics Team 1510
Team 1510 co-founder
Former Team 955 member
Curie lives on in my heart <3