You don't do any drilling in the bumper. There's already holes in the aluminum where those plastic inserts to hold the screws go. You only drill through the center trim strip.
You need a different trim center trim strip part #51112232451. Then get the bracket, screws, washers, & inserts (parts 12, 18, 19, & 21 in diagram). I'll try looking through my paperwork to see if I still have the receipt for the bracket & stuff so I can get a part # for the inserts for you.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build