Kindly please advise the following:-
Original (othermake) gearbox reduction is 1:8 (from your photo) and output from gearmotor should be around 180rpm (1440/8) however your enquiry indicated 165rpm (ratio =8.59).
For this case, do you want us to change order to 183rpm (ratio =7.74) where the speed is the closest to 180rpm (torque would not be an issue) ?
Kindly please confirm whether you needed 165rpm or 180rpm.