Reducing back box for Ring Elite mount

Hello, Thank you in advance for the help. I have an existing door station that I am switching out to install the Elite. The back box for the existing is significantly larger (6.1" X 4/1" X 3). I was looking for a reducer for weeks but can't locate. Now exploring havinv my contractor fill in the void and installing a junction box for the Elite. Can anyone provide the junction box dimemsions and the part list I need to order?I would also like the 30 degree mount. Thanks again.