Replacing Nutone with Pro

Hi - I have an installation issue.I am attempting to replace my Nutone intercom/doorbell with a Pro model. My exterior is brink and there is a rough-in housing that the intercom speaker/doorbell sits in. An adapter face plate is available which will cover this housing unit (5"x7") in order to support a Ring conversion. The problem I am facing is the screws to mount to the housing unit are too big to pass thru the hole on the Ring unit. And it I use the screws that came with Ring, they are too small (diameter wise) to fit threads of the housing unit. What are my options?