I will see what 89mm converts to. What type of construction is the box going to be mounted to? Wood, metal or other. We have cut-in style, nail on style for wood and metal studs. Once I know what it is being installed onto then can tell you what you will need. I will also talk to my supplier and tell him. I'll give you the phone number and email of who to contact and you can deal with him directly. You will need to place the order with a credit card and then they can ship it to you. Let me know and I will pass on the information. I can also walk you through the make up stage if you need help. Larry