roll bar installation

Hi, I am looking for the driver and passenger roll hoop support brackets. I have the roll hoops and associated plastic, just missing these two items.

Help required please. I have purchased a second hand S/S XSPower roll bar for my 1998 Z3 but the diameter of the tube section that is inserted into the seat belt retraction cover is larger than the hole ? Is this standard ? it must be possible to enlarge it but will it fit into the metal base...